NASA Commercial Crew Program: Schedule Uncertainty Persists for Start of Operational Missions to the International Space Station

In 2014, NASA awarded two firm-fixed-price contracts to Boeing and SpaceX, worth a combined total of up to $6.8 billion, to develop crew transportation systems and conduct initial missions to the ISS. In July 2018, GAO found that both contractors continued to delay their certification dates and that further delays were likely. NASA must certify the contractors' crew transportation systems before the contractors can begin operational missions to the ISS. The contractors were originally required to provide NASA all the evidence it needed to certify that their systems met its requirements in 2017.

The House Committee on Appropriations included a provision in its 2017 report for GAO to continue to review NASA's human space exploration programs. This is the latest in a series of reports addressing the mandate. This report examines the extent to which the Commercial Crew Program and its contractors have made progress towards certification.

To do this work, GAO analyzed contracts, schedules, and other documentation and spoke with officials from the Commercial Crew Program, Boeing, and SpaceX.

Both of the Commercial Crew Program's contractors, Boeing and SpaceX, have made progress on their crew transportation systems. However, neither is ready to begin carrying astronauts into space as both continue to experience delays to certification. Certification is a process that the National Aeronautics and Space Administration (NASA) will use to ensure that each contractor's spacecraft, launch vehicle, and ground support systems meet its requirements for human spaceflight before any operational missions to the International Space Station (ISS) can occur. Factors contributing to schedule uncertainty include:

Fluctuating schedules. As the contractors continue to build and test hardware—including SpaceX's March 2019 uncrewed test flight— their schedules for certification change frequently. As of May 2019, both contractors had delayed certification nine times, equating to more than 2 years from their original contracts (see figure). This includes several delays since GAO last reported in July 2018.

Program Workload. NASA's ability to process certification data packages for its two contractors continues to create uncertainty about the timing of certification. The program has made progress conducting these reviews but much work remains. In addition, the program allowed both contractors to delay submitting evidence that they have met some requirements. This deferral has increased the amount of work remaining for the program prior to certification.

In February 2019, NASA acknowledged that delays to certification could continue, and announced plans to extend U.S. access to the ISS through September 2020 by purchasing seats on the Russian Soyuz vehicle. However, this arrangement does not fully address GAO's July 2018 recommendation to develop a contingency plan for ensuring access to the ISS until a Commercial Crew Program contractor is certified. NASA concurred with the recommendation but has not yet implemented it. Continued NASA attention on this issue is needed given the uncertainty associated with the final certification dates.

GAO continues to believe that NASA should develop a contingency plan to ensure uninterrupted access to the ISS if delays persist beyond September 2020. NASA generally agreed with GAO's findings.

Following the retirement of the Space Shuttle in 2011, the United States  was left with no domestic ability to provide crew access to the  International Space Station (ISS). Since then, the National Aeronautics  and Space Administration (NASA) has relied on obtaining seats on the  Russian Soyuz spacecraft to maintain a U.S. presence on the station.  NASA’s Commercial Crew Program is facilitating the commercial  development of a crew transportation system that can provide safe,  reliable, and cost-effective transportation to and from the ISS and that  would end this dependency. NASA’s goal is to have one or more  contractors that can provide crew transportation services to the ISS.  NASA plans for the ISS to be operational until at least 2024.

NASA’s acquisition strategy for the Commercial Crew Program is similar  to the one it used on the Commercial Cargo Program, but different from  other spacecraft it has built for humans, from Mercury to Gemini and  Apollo to the Space Shuttle. Under the Commercial Crew Program, each  contractor designs, develops, builds, owns, and operates its spaceflight  system and infrastructure. The contractors have access to NASA’s  expertise and resources throughout the development process; but NASA  engineers are not the ones making design decisions and NASA personnel  are less involved in processing, testing, launching, and operating the crew  transportation system. In addition, NASA must certify the contractors’  spacecraft, launch vehicle, and ground support systems before the  contractors can begin operational missions to the ISS. Certification is the  process that NASA will use to ensure that the contractors’ systems meet  its requirements for human spaceflight. In the end, NASA will buy a crew  transportation service—a ride for its astronauts to and from the ISS.

The House Committee on Appropriations included a provision in its 2017  report for GAO to continue to review NASA’s human space exploration  programs, including the Commercial Crew Program. This report is the  latest in a series of reports addressing the mandate. This report examines  the extent to which the contractors and program have made progress  towards certification.

We reviewed program and contract documents, including quarterly  progress updates, monthly risk charts, and monthly schedule summaries  from August 2018 through April 2019. We also interviewed program and  contractor officials to identify steps being taken to mitigate selected risks  and assess the extent of cost or schedule impacts if the risks were to be  realized. To select the risks, we examined the program’s risk charts and  identified the top five risks for each contractor that also had a safety  component. We took this approach because the contractors are nearing  test flights that will include crewmembers. In addition, we followed up on  risks that we reviewed in our July 2018 report. These included Boeing’s  spacecraft forward heat shield and SpaceX’s propellant loading  procedures, redesigned launch vehicle vessel, and engine turbine  cracking.

To determine the extent to which the certification milestone has been  delayed over time, we analyzed the contractors’ schedule data from  quarterly progress reports and program documents from the first quarter  of calendar year 2015 through the second quarter of calendar year 2019.  Second quarter of calendar year 2019 data was the most recent data at  the time of our analysis. We selected the certification milestone because  it determines whether the crew transportation system meets the  Commercial Crew Program’s requirements. We also analyzed program  data for each contractor to determine how many safety reports and  certification packages each contractor submitted and how many the  program had approved as of April 2019. We assessed the reliability of the  data by interviewing program officials and manually testing the data, and  deemed it reliable for the purpose of reporting on the program’s workload.

We conducted this performance audit from August 2018 to June 2019 in  accordance with generally accepted government auditing standards.  Those standards require that we plan and perform the audit to obtain  sufficient, appropriate evidence to provide a reasonable basis for our  findings and conclusions based on our audit objectives. We believe that  the evidence obtained provides a reasonable basis for our findings and  conclusions based on our audit objective.

NASA awarded firm-fixed-price contracts in 2014 to Boeing and SpaceX,  valued at up to $4.2 billion and $2.6 billion, respectively, for the  development of crew transportation systems that meet NASA  requirements and for the initial service missions to the ISS.

Figure 1 shows the spacecraft and launch vehicles for Boeing and  SpaceX’s crew transportation systems.

These contracts encompass the firm-fixed-price design, development,  test, and evaluation work needed to support NASA’s certification of the  contractors’ spacecraft, launch vehicle, and ground support systems and  begin operational missions to the ISS.

The Commercial Crew Program manages two processes in order to  support the contractors’ uncrewed test flight, crewed test flight, and  certification milestone. The contractors must submit evidence, which the  Commercial Crew Program must review and approve for both processes.

A three-phased safety review process informs the program’s quality  assurance activities and is intended to ensure that the contractors  have identified all safety-critical hazards and implemented associated  controls prior to the first crewed test flight.

In phase one, the contractors identify risks in their designs and  develop reports on potential hazards, the controls they put in  place to mitigate them, and explanations for how the controls will  mitigate the hazards.

In phase two, the program reviews and approves the contractors’  hazard reports and develops strategies to verify and validate that  the controls are effective.

In phase three, the contractors will conduct the verification  activities and submit the hazard reports to the program for  approval.

The verification closure notice process is used to verify that the  ISS requirements, applicable to any spacecraft flying to the ISS,  and

After the contractor has successfully completed its uncrewed and crewed  test flights and the above processes, the program determines at the  contractor’s certification milestone whether the crew transportation  system meets NASA’s requirements for human spaceflight. Following this  contract milestone is an agency certification review, which authorizes the  use of a contractor’s system to transport NASA crew to and from the ISS.  It is at this point that the contractors can begin operational missions.  Figure 2 shows the path leading to operational missions.

Contractors Are Making Progress on Vehicles, but Certification Date Remains Unclear

Both contractors have made progress building and testing hardware,  including SpaceX’s uncrewed test flight. But continued schedule delays  and remaining work for the contractors and the program create continued  uncertainty about when either contractor will be certified to begin  conducting operational missions to the ISS. The program has made  progress reviewing the contractors’ certification paperwork, but contractor  delays in submitting evidence for NASA approval may compound a ‘bow  wave’ of work, which creates uncertainty about when either contractor will  be certified. NASA acknowledged the schedule uncertainty in February  2019, when it announced plans to purchase two additional Soyuz seats  from Russia, citing concerns about the difficulties associated with  achieving first flights in the final year of development.

Construction and Testing of Contractors’ Hardware Is Progressing

Both contractors are building several spacecraft, some of which are near  completion. Each contractor’s spacecraft includes two main modules:

Boeing’s spacecraft—CST-100 Starliner—is composed of a crew  module and a service module. The crew module will carry the crew  and cargo. It also includes communication systems, docking  mechanisms, and return systems for Earth landing. The service  module provides propulsion on-orbit and, if needed, in abort  scenarios—when a failure prevents continuation of the mission and a  return is required for crew survival—as well as radiators for thermal  control.

SpaceX’s spacecraft—Dragon 2—is composed of a capsule, which  we refer to as the crew module, and a trunk, which we refer to as the  support module. The crew module will carry the crew and cargo. It  also includes avionics, docking mechanisms, and return systems for a  water landing. The support module includes solar arrays for on-orbit  power and guidance fins for escape abort scenarios.

Different spacecraft will be used for the uncrewed test flight and the  crewed test flight, as well as to support other test events. See table 1 for  a description of each contractor’s hardware builds, current status, and  upcoming events.

Additional details on select hardware testing follow.

In June 2018, Boeing experienced an anomaly while testing its  launch abort engines. During a test firing, four of the eight total valves  in the four launch abort engines failed to close after a shutdown  command was sent. In response to this event, Boeing initiated an  investigation to identify the root cause. According to Boeing officials,  Boeing plans to replace components on all of its service modules  except for the uncrewed test flight service module. This is because  the abort system will not be active for the uncrewed test flight. Boeing  plans to resume testing its launch abort engines in May 2019. A  NASA official told us that addressing this anomaly and identifying its  root cause resulted in a 12-month schedule delay to launch abort  propulsion system testing.

In March 2019, SpaceX conducted its uncrewed test flight, which  demonstrated that the capsule could dock with the ISS and return to  Earth. NASA officials described SpaceX’s uncrewed test flight as a  success with key systems such as the guidance, navigation, and  control and the parachutes performing as expected. A SpaceX official  told us that this was a very successful test and represented significant  risk reduction from a schedule and technical perspective.  Subsequently, the spacecraft used in the uncrewed test flight was  destroyed in a testing anomaly. The anomaly occurred during a test  that SpaceX was conducting in advance of an in-flight abort test  scheduled for this summer. As of May 2019, SpaceX was  investigating the anomaly.

Repeated Delays and Remaining Work Create Continued Uncertainty for Certification

Continued schedule delays create uncertainty about when NASA will  certify either contractor to begin conducting operational missions to the  ISS. We have previously found that the contractors’ schedules regularly  changed, and this pattern continues. As of May 2019, both contractors  have delayed their certification milestone nine times since establishing  dates in their original contracts. In the span of less than a year, since our  July 2018 report, Boeing has again delayed its certification milestone four  times and by 12 months, while SpaceX has again delayed its certification  milestone three times and by 7 months. Both contractors are now  planning for certification to occur more than 2 years beyond the original  dates in their contracts–Boeing in January 2020 and SpaceX in  September 2019, though this date is under review and could further slip  (see figure 3).

Over time, both program and contractor officials have told us that they  struggle to establish stable schedules. In 2018, the Commercial Crew  Program manager told us that she relied on her previous experience to  estimate schedule time frames as opposed to relying on the contractors’  schedules, which were overly optimistic. In March 2019, a senior NASA  official told us that the agency has struggled to establish schedules with  both contractors, often needing to negotiate dates with senior company  officials. Further, SpaceX officials explained that they would not know the  schedule for the crewed test flight until they conducted the uncrewed test  flight. However, even having conducted the uncrewed test flight in March  2019 and before the April 2019 anomaly, SpaceX and NASA were still re- evaluating the schedule for the crewed test flight.

Contractors’ Technical Risks Create Continued Uncertainty for Certification

Both contractors are continuing to mitigate technical risks identified by  program officials that need to be addressed in order to reach certification.  The program will close a risk when the contractor is able to fully mitigate  it. If all mitigation activities are exhausted, but a risk still remains, the  program will determine if the risk is acceptable as part of the agency’s  rationale for flight. As the contractors address these technical risks and  proceed through integration and testing, any issues that arise during  testing or the test flights could further delay certification.

Parachute System Certification. Boeing is conducting five  parachute system qualification tests to demonstrate that its system  meets the Commercial Crew Program’s requirements, which will be  validated on two spacecraft flight tests. However, in August 2018,  Boeing identified a faulty release mechanism for its drogue  parachute—which initially slows down the capsule—during its third  parachute qualification test that successfully deployed all parachutes.  Identifying and fixing the faulty mechanism delayed its fourth  parachute qualification test. According to a NASA official, Boeing is  conducting testing to qualify an alternative design, and Boeing must  qualify this alternative design before the crewed test flight.

Launch Vehicle Engine Anomaly. Boeing is addressing a safety risk  related to a launch vehicle component. Specifically, during a 2018  launch, the launch vehicle engine position during ascent deviated  from commands but the launch vehicle provider stated that it achieved  all mission objectives. Program officials told us that they have insight  into the launch vehicle manufacturer’s ongoing investigation and have  participated in a separate independent review team. Boeing will  implement a set of corrective actions for the uncrewed test flight, and  will continue testing the engines for the crewed test flight.

Spacecraft-Generated Debris. Boeing is addressing a risk that under  normal operating procedures the initiators that trigger separation  events, such as the separation of the crew and service module prior to  re-entry, may generate debris and damage the spacecraft. These  components function as expected, but Boeing plans to install  hardware to contain debris generated when the initiators fire. Program  officials told us that they believe Boeing has identified a solution that  will be sufficient for the uncrewed and crewed test flights, but the  program is continuing to explore a possible redesign for future  operational missions.

Spacecraft Forward Heat Shield. We had previously found that  Boeing was addressing a risk that during descent a portion of the  spacecraft’s forward heat shield may re-contact the spacecraft after it  is jettisoned and damage the parachute system. Since our last  report, Boeing tested the performance of the forward heat shield in  worst-case scenarios and found there was no damage to the  parachute system or the spacecraft. After reviewing test data, the  program determined that Boeing had completed the mitigation  activities and, as of February 2019, no additional steps were needed.

Parachute System Certification. Like Boeing, SpaceX is conducting  several parachute tests to demonstrate that its system meets the  Commercial Crew Program’s requirements. However, SpaceX  experienced two anomalies with its parachute system in August 2018.  As a result, a SpaceX official told us they enhanced the parachute  design to improve robustness. NASA officials told us SpaceX’s  enhanced parachutes performed well on its uncrewed test flight. Prior  to the crewed test flight, SpaceX must demonstrate the performance  of its parachute system. SpaceX plans to continue to test its  parachutes, and according to a SpaceX official, will take all steps  necessary to ensure that the flight design meets or exceeds minimum  performance levels.

Propellant Loading Procedures. SpaceX is continuing to address a  safety risk related to its plans to conduct launch vehicle propellant  loading procedures after the astronauts are on board the spacecraft.  SpaceX officials told us that this loading process has been used in  other configurations for multiple SpaceX flights. The Commercial  Crew program has approved SpaceX’s proposed loading procedures,  including the agreed upon demonstration of the loading procedure five  times from the launch site in the final crew configuration before the  crewed test flight. The five events include the uncrewed test flight and  in-flight abort test. As of March 2019, SpaceX had completed the first  two events.

Redesigned Composite Overwrap Pressure Vessel. SpaceX is  continuing to address a risk that its launch vehicle’s redesigned  composite overwrap pressure vessel, which is intended to contain  helium under high pressure, may serve as an ignition source. The  program and SpaceX conducted tests on the redesigned vessel and  the program determined that all possible ignition sources, with one  exception, have a low likelihood of creating ignition. The program  continues to assess this ignition source. According to a NASA official,  there were no indications of any issues during SpaceX’s uncrewed  test flight. SpaceX officials also told us that the redesigned vessel has  successfully flown on multiple flights. The program will need to  determine whether to accept the risk associated with this technical  issue prior to SpaceX’s crewed test flight.

Engine Turbine Cracking. NASA continues to assess a SpaceX risk  related to the design of its launch vehicle engines, which has  previously resulted in the turbine wheel cracking. To mitigate the  turbine cracking risk, SpaceX conducted additional qualification  testing and developed an operational strategy that resulted in no  cracks. Consequently, the program accepted this risk for SpaceX’s  uncrewed test flight but levied a constraint on the crewed test flight.  Specifically, SpaceX has agreed to conduct a follow-on test campaign  of the engines to demonstrate that it meets NASA’s standards in order  to launch its crewed test flight. Program officials said SpaceX plans to  build the launch vehicle engines for its crewed test flight concurrently  with this follow-on testing series.

Program Office Workload Is a Continued Schedule Risk to Certification

The Commercial Crew Program’s ability to process certification data  packages for its two contractors continues to create uncertainty about the  timing of certification. Specifically, the program is concurrently reviewing  and approving both contractors’ phased safety reviews and verification  closure notices. We previously reported that program officials, the  contractors, and independent review organizations had concerns about a  “bow wave” of work for the program. For example, at that time, the  program’s safety and mission assurance office identified the upcoming  bow wave of work in a shrinking time period as a top risk to achieving  certification.

Three-Phased Safety Reviews. The program continues to make  progress conducting its phased safety reviews, but it has not yet  completed them. In February 2017, we found that the program was  behind schedule completing its phased safety reviews and, as of April  2019, it had yet to complete this process. As shown in Table 2, the  program is near completion of phase two reviews and phase three  reviews are in progress.

Program officials told us that they have started work on many of the  phase three safety reviews, but the data only reflect their efforts once  they complete a phased safety report in its entirety. Any additional delays  to complete this process, however, would delay the crewed test flights  and create uncertainty about when NASA will certify the contractors to  begin operational flights.

Verification Closure Notices. NASA has made progress verifying that  the contractors have met ISS and Commercial Crew Program  requirements, but much work remains. When a contractor is ready for  NASA to verify that it has met a requirement, such as that the contractor’s  system can detect and alert the crew to critical faults that could result in a  catastrophic event, the contractor submits data for NASA to review  through a verification closure notice. Table 3 shows the agency’s  progress approving verification closure notices for each contractor.

Program officials told us that, because the contract solicitation did not  require an uncrewed test flight, they had not previously determined the  minimum number of Commercial Crew Program requirements that the  contractors should meet prior to an uncrewed test flight. Subsequently,  both contractors included an uncrewed test flight as part of their  schedules. As these test flights approached, NASA determined that it  must verify that the contractors met approximately 20 percent of the  program’s requirements before the contractors’ uncrewed test flight and  the remaining 80 percent before the contractors’ crewed test flights. The  program made this determination based on ensuring the contractors met  requirements related to the spacecraft safely approaching and docking to  the ISS; ensuring the safety of the ISS and its crew; and meeting any  mission-specific requirements for cargo.

Both contractors originally planned for the program to verify they had met  more than 20 percent of the Commercial Crew Program requirements  before the uncrewed test flight but have subsequently changed their  plans. For both contractors, the program is allowing the contractors to  submit more verification closure notices between the uncrewed and  crewed test flight than initially envisioned. Program officials told us that  contractors proposed deferring the submission of verification closure  notices because they were having difficulties meeting the original targets.  Figure 4 includes SpaceX and Boeing’s original and current plans for  verification of requirements compared to the Commercial Crew Program’s  minimum level of requirements it determined was necessary for the  uncrewed test flight. As reflected in the figure, these new plans, which  defer submission of work to the crewed test flight, may compound the  program’s bow wave of work and create uncertainty about the timing of  certification.

Further, the Commercial Crew Program will need to reassess a subset of  requirements closed for the uncrewed test flight prior to the crewed test  flight. For example, of the 78 requirements Boeing plans to close prior to  the uncrewed test flight, the program will re-assess 16; for SpaceX’s 49  requirements, the program will re-assess 32. Program officials told us that  some of this work is expected based on known changes to the  contractors’ systems between the uncrewed and crewed test flight. For  example, officials told us that they approved a verification closure notice  for SpaceX’s air conditioning system in order to support the uncrewed test  flight, but they know that they will need to re-assess it because SpaceX is  making changes before its crewed test flight. While these types of  changes and those that are identified through testing are not uncommon,  they further add to the program’s workload and create uncertainty about  the timing of certification.

Among the requirements that must be closed before the crewed test flight  is loss of crew, which is a metric that captures the probability of death or  permanent disability to one or more crew members. According to program  risk charts, the program’s top safety risk continues to be that neither  contractor will meet the contractual requirement of a 1 in 270 probability  of incurring loss of crew. We previously found that NASA lacked a  consistent approach for how to assess loss of crew and recommended  that key parties, including the program manager, collectively determine  and document how the agency will determine its risk tolerance level prior  to certifying either contractor. NASA partially concurred with that  recommendation, stating that, if neither contractor can meet the loss of  crew requirement, the program will request a waiver through the human  rating certification process to ensure transparency. As of March 2019,  NASA officials told us they have not taken steps to address this  recommendation. Officials told us that the Commercial Crew Program is  currently reviewing Boeing’s loss of crew verification closure notice and  SpaceX’s draft verification closure notice in order to verify if the  contractors have met the loss of crew requirement.

According to program officials, one of the biggest challenges for the  program is balancing its workload to support the two contractors, but  officials are making an effort to review each contractor’s data products as  they are submitted. For example, program officials told us that they were  able to review SpaceX submissions during the summer of 2018, while  Boeing’s submissions slowed as it focused on addressing the test  anomaly with its launch abort engines. However, based on current  schedules, the program must complete its reviews of certification  paperwork while supporting uncrewed, crewed, and abort system test  flights for both contractors before the end of 2019. Both contractors said  they have concerns about NASA’s ability to maintain its pace of  processing paperwork in order to support the contractors’ planned test  flights and certification dates. The potential bow wave of work continues  to create uncertainty about the timing of certification for either contractor,  which could result in delays to the first operational mission to the ISS.

NASA Is Taking Steps to Mitigate Delays to Start of Operational Missions

In February 2019, NASA announced plans to buy two more Soyuz seats  from Russia, thereby acknowledging that delays to certification of the  Commercial Crew Program contractors could continue. These seats  would extend U.S. access to the ISS from November 2019 through  September 2020. According to a senior NASA official, NASA is not  purchasing a new Soyuz spacecraft, which we have previously found  requires a 3-year lead time. Instead, two additional seats became  available on existing vehicles after changes to the Soyuz manifest. In  2015, NASA paid approximately $82 million per seat through its contract  with the Russian Federal Space Agency (Roscomos). Program officials  stated they could not publicly disclose the price NASA paid for these two  new additional seats, but noted that the cost was 5 percent higher per  seat than the previous contract modification to purchase Soyuz seats and  is consistent with inflation.

In addition, NASA plans to extend the duration of Boeing’s crewed test  flight. In March 2018, NASA modified its contract with Boeing to allow  NASA to add a third crew member and extend the length of the crewed  test flight. In July 2018, we reported that NASA was considering this  option as one way to maintain a U.S. presence on the ISS, but noted it  had limited usefulness if Boeing’s crewed test flight slipped past the  return date of the last Soyuz flight.

NASA’s actions—purchasing the two additional Soyuz seats and  implementing an extended duration crewed test flight for Boeing—do not  fully address our July 2018 recommendation to develop and maintain a  contingency plan for ensuring a presence on the ISS until a Commercial  Crew Program contractor is certified. NASA concurred with this  recommendation but, to fully implement it, NASA needs to provide  additional support regarding planning efforts to ensure uninterrupted  access to the ISS if delays with the Commercial Crew Program  contractors continue beyond September 2020. Continued NASA attention  on this issue is needed given the uncertainty associated with the final  certification dates.

We provided a draft of this product to NASA for comment. In its response,  reproduced in appendix I, NASA generally agreed with our findings and  included an update on the progress made by Boeing and SpaceX. NASA  also provided technical comments, which we incorporated as appropriate.

We are sending copies of this report to NASA Administrator and  interested congressional committees. In addition, the report is available at  no charge on the GAO website at http://www.gao.gov.

If you or your staff have any questions about this report, please contact  me at (202) 512-4841 or chaplainc@gao.gov. Contact points for our  Offices of Congressional Relations and Public Affairs may be found on  the last page of this report. GAO staff who made major contributions to  this report are listed in appendix II.

Appendix I: Comments from the National Aeronautics and Space Administration

Appendix II: GAO Contact and Staff Acknowledgments

Cristina T. Chaplain at (202) 512-4841 or chaplainc@gao.gov.

In addition to the contact named above, Molly Traci, Assistant Director;  Lorraine Ettaro; Laura Greifner; Kurt Gurka; Joy Kim; Christopher Lee;  Katherine Pfeiffer; Roxanna T. Sun; Hai Tran; Kristin Van Wychen; and  Alyssa Weir made significant contributions to this report.

NASA contracted with two companies, Boeing and SpaceX, to develop vehicles to transport astronauts to the International Space Station.

Before any missions can happen, NASA will have to certify that both contractors' vehicles are safe for human spaceflight. But both contractors have run into chronic delays. While both contractors originally planned to be certified in 2017, now neither is expected to be ready until late 2019 at the earliest.

NASA has bought seats on a Russian vehicle to ensure U.S. access to the space station through September 2020, but does not have a plan if delays persist past then.