To Do The Heavy Lifting
Paul D. Spudis
A recent talking points memo by the Office of Science and Technology Policy (OSTP) seeks to clarify some aspects of the new direction in regards to the cancelled Project Constellation. Touted by some as "compromise," it asserts that NASA will develop and build a new "Orion lite" crew vehicle whose primary mission will be to serve as an escape pod for the crew of the International Space Station (ISS). And more interestingly, the policy "Begins major work on building a new heavy lift rocket sooner, with a commitment to decide in 2015 on the specific heavy-lift rocket that will take us deeper into space."
I'm confused. If a heavy lift launch vehicle (HLLV) is not needed for future human missions beyond LEO, why are we spending billions of dollars researching aspects of it in order to make a design decision five years hence? If a heavy lift launch vehicle is needed for such missions, why are we waiting five years to make that decision when we have the parts and workforce needed to make the vehicle now?
Are you confused?
Let's break this down a bit. What exactly is a heavy lift launch vehicle and what is its significance to spaceflight and more specifically, to sending people beyond low Earth orbit (LEO)? The Space Shuttle orbiter carries a bit more than 24 metric tonnes (mT; 52,800 lbs.) to orbit. That would seem to qualify as heavy lift. But the old Saturn V could launch 118 mT (260,000 lbs.) to low Earth orbit. That capability allowed us to launch the complete Apollo spacecraft (three modules) and its Earth departure stage (S-IVB) in one fell swoop. The cancelled Ares V launch vehicle was to have carried up to 188 mT to LEO (over 400,000 lbs). These indeed are heavy lift launchers.
Why do we need heavy lift? On this topic, thought among space engineers falls into two broad categories - those who think that heavy lift of the Saturn V variety (~100 mT to LEO) is the sine qua non for human missions beyond LEO, and those who think we can develop an incremental approach that uses the smaller vehicles currently available, such as the medium-lift class Atlas V (21 mT to LEO) and Delta IV-Heavy (25.8 mT to LEO) launchers. The basic philosophical difference centers around what can be done in space versus what has to be done on Earth.
The Saturn V was built so that a single, self-contained lunar mission could be launched on one vehicle. This meant that the crew could focus their efforts solely on their lunar voyage and not have to concern themselves with assembling a larger, more complex vehicle in Earth orbit. In modern terms of human flight beyond LEO, the big advantage of heavy lift is that you can use fewer launches to get the same amount of equipment and material in space, thus reducing the chance that a single launch failure might cause a mission abort. Propellant can "boil off" in space, especially the very cold (cryogenic) liquid oxygen and hydrogen that fuel the most powerful chemical rockets. It is also assumed that assembling a few large pieces in space is simpler than assembling many more smaller ones. But now we've learned quite a bit about assembly in space from construction of the ISS.
Critics of new heavy lift vehicle development point to the high costs associated with new vehicle development. They also point out that there are new techniques and technologies that can help us venture into the Solar System with existing launch vehicles. One of those ideas are depots where propellant is collected and used to fuel empty vehicles for journeys beyond LEO. A detailed architecture that features propellant depots and that does not require a new heavy lift vehicle has already been published. Many groups strongly advocate this approach.
Which brings us back to the new OSTP document. This new document indicates that work will proceed on development of a heavy lift launch vehicle, with a decision on what vehicle to build coming in 2015 (
note well: not building a vehicle, but making a decision on
what vehicle to build). How will our decision on heavy lift be more informed in five years than it is now?
In five years, all the Shuttle manufacturing and assembly infrastructure, including tooling dies, assembly jigs, milling facilities and solid-rocket booster production lines will have been disassembled, mothballed or discarded. Some of this shutdown has already begun. The skilled workforce that now builds and operates the Shuttle launch system will dissipate (people have families to support and cannot stand around waiting for a decision five years - maybe never - down the road). There will be no experience base to build, assemble and launch a heavy-lift vehicle within NASA or industry.
I have written previously that a Shuttle-derived heavy lift vehicle can be built now, with existing piece parts and minimal changes to the assembly and launch infrastructure at Michoud and the Cape. Such a vehicle can launch 80 mT to LEO; two launches can send a human mission to the Moon. And it is completely affordable, fitting into the existing run-out budget and available for use within a few years. Currently, robotic missions are discovering and analyzing the vast resources of the Moon. More robotic missions are needed to begin the processing of lunar resources in preparation for human return and expansion beyond LEO. These are all things NASA can afford to do now.
This re-invention of NASA, as trickled out by the administration, has been eagerly seized upon by many in the "New Space" community, as their long sought, free-market (but government funded - for now) opening at building a commercial rocket industry. Some of us (who also believe in free markets) see different motives for this new direction and are particularly concerned that the new "
flexible path (FP)" doesn't have any specified destination or mission.
The fundamental fecklessness of the new direction is exposed in this new OSTP document; we will build a Crew Return Vehicle for ISS that is not needed (if we can get there on the Soyuz, we can certainly return on it) and we will conduct "research" on heavy lift technologies that are already well understood.
Maybe it's not so confusing after all.
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About Paul D. Spudis
Paul D. Spudis is a senior staff scientist at the Lunar and Planetary Institute in Houston, Texas. His website can be found at . The opinions expressed here are his own and do not reflect the views of the Smithsonian Institution or his employer.