<story><title>Webb flies Ariane 5: watch the launch live on 25 December</title><url>https://www.esa.int/Science_Exploration/Space_Science/Webb/Webb_flies_Ariane_5_watch_the_launch_live</url></story><parent_chain><item><author>onphonenow</author><text>What I don&amp;#x27;t understand is for $11 billion - can&amp;#x27;t we do 3 $3B space telescopes that work reasonably well? Spread risk? More science?&lt;p&gt;Let&amp;#x27;s say a Falcon 9 launch is $90M. Falcon heavy let&amp;#x27;s say $200M.&lt;p&gt;So you take your 3x $3B. Put $200M&amp;#x2F;instrument into launch, have $2.8B per telescope leftover.&lt;p&gt;There just seems to be something wrong that it costs THIS much to build a telescope.&lt;p&gt;That said, the Thirty Meter Telescope is also a sort of &amp;quot;forever&amp;quot; job, the delays have stretched on and on.&lt;p&gt;I wonder if you did something like bid out and paid just on performance instead of this forever cost reimbursement thing. Right now if you can get onto one of these mega projects, and can stretch it out with delays, it basically can cover your career (ie, 20 year projects).</text></item><item><author>wslack</author><text>I suggest the book &amp;quot;Failure is not an option&amp;quot; by Gene Kranz, an Apollo flight director (played by Ed Harris in Apollo 13). He describes how the primary work of flight controllers in all missions is risk management. You are constantly balancing mission needs, fuel needs, mass needs, temperature needs, and etc etc.&lt;p&gt;I don&amp;#x27;t think that a raw metric of the number of SPOF is the right way to measure the risk of this spacecraft. It&amp;#x27;s a fun term for PR purposes (and emphasizing the risk here) but the actual risk posture is more complex.&lt;p&gt;I imagine that in the course of developing this, they worked out a possible strategy without all of those SPOF - but doing so doesn&amp;#x27;t eliminate the risk, and the impact to mission is likely massive.</text></item><item><author>dimtion</author><text>I do have a question about JWST that I wasn&amp;#x27;t able to find a fine answer in other forums.&lt;p&gt;A lot of people and engineers are saying that the JWST is a marvel of engineering, with truly inovative technical solutions and a giant step up compared to Hubble Telescope. And it does seems like so!&lt;p&gt;However, I&amp;#x27;m always baffled how everyone seems proud that the telescope has something like 200 SPOF during deployment, and if even one of them fails the whole mission could fail.&lt;p&gt;I know that each step has probably been throughoutly tested, and that the acceptable probability of failure of each one of those steps has been deemed acceptable. But I&amp;#x27;m still surprised that people are proudly conflating excellent engineering with a design that has a large number of spofs.&lt;p&gt;In my domain this would be considered as a terrible design (aka &amp;quot;hope is not a strategy&amp;quot;), even given the constraints of mass and volume that such project incur: 200 hundred low probability events, chained, can get in the realm of possible.&lt;p&gt;I can&amp;#x27;t imagine JSWT team doing &amp;quot;bad engineering&amp;quot;, so I&amp;#x27;m sure I&amp;#x27;m missing a piece. Is it only PR that underline this aspect? Is JWST as brittle as the news want to make us think? Or are there technical reasons or acceptable failure modes that gives confidence that those steps are not as critical as the news let us people know?</text></item></parent_chain><comment><author>sjburt</author><text>There are many people in NASA and around that have made similar arguments.&lt;p&gt;I think the real reason that they never have a lot of traction, sadly, is that if you propose 3, Congress will give you 2. And then when 2 are over budget, it will get trimmed to one. Better to propose one big mission and get it to the point where it can’t be cut easily.</text></comment>
<story><title>Webb flies Ariane 5: watch the launch live on 25 December</title><url>https://www.esa.int/Science_Exploration/Space_Science/Webb/Webb_flies_Ariane_5_watch_the_launch_live</url></story><parent_chain><item><author>onphonenow</author><text>What I don&amp;#x27;t understand is for $11 billion - can&amp;#x27;t we do 3 $3B space telescopes that work reasonably well? Spread risk? More science?&lt;p&gt;Let&amp;#x27;s say a Falcon 9 launch is $90M. Falcon heavy let&amp;#x27;s say $200M.&lt;p&gt;So you take your 3x $3B. Put $200M&amp;#x2F;instrument into launch, have $2.8B per telescope leftover.&lt;p&gt;There just seems to be something wrong that it costs THIS much to build a telescope.&lt;p&gt;That said, the Thirty Meter Telescope is also a sort of &amp;quot;forever&amp;quot; job, the delays have stretched on and on.&lt;p&gt;I wonder if you did something like bid out and paid just on performance instead of this forever cost reimbursement thing. Right now if you can get onto one of these mega projects, and can stretch it out with delays, it basically can cover your career (ie, 20 year projects).</text></item><item><author>wslack</author><text>I suggest the book &amp;quot;Failure is not an option&amp;quot; by Gene Kranz, an Apollo flight director (played by Ed Harris in Apollo 13). He describes how the primary work of flight controllers in all missions is risk management. You are constantly balancing mission needs, fuel needs, mass needs, temperature needs, and etc etc.&lt;p&gt;I don&amp;#x27;t think that a raw metric of the number of SPOF is the right way to measure the risk of this spacecraft. It&amp;#x27;s a fun term for PR purposes (and emphasizing the risk here) but the actual risk posture is more complex.&lt;p&gt;I imagine that in the course of developing this, they worked out a possible strategy without all of those SPOF - but doing so doesn&amp;#x27;t eliminate the risk, and the impact to mission is likely massive.</text></item><item><author>dimtion</author><text>I do have a question about JWST that I wasn&amp;#x27;t able to find a fine answer in other forums.&lt;p&gt;A lot of people and engineers are saying that the JWST is a marvel of engineering, with truly inovative technical solutions and a giant step up compared to Hubble Telescope. And it does seems like so!&lt;p&gt;However, I&amp;#x27;m always baffled how everyone seems proud that the telescope has something like 200 SPOF during deployment, and if even one of them fails the whole mission could fail.&lt;p&gt;I know that each step has probably been throughoutly tested, and that the acceptable probability of failure of each one of those steps has been deemed acceptable. But I&amp;#x27;m still surprised that people are proudly conflating excellent engineering with a design that has a large number of spofs.&lt;p&gt;In my domain this would be considered as a terrible design (aka &amp;quot;hope is not a strategy&amp;quot;), even given the constraints of mass and volume that such project incur: 200 hundred low probability events, chained, can get in the realm of possible.&lt;p&gt;I can&amp;#x27;t imagine JSWT team doing &amp;quot;bad engineering&amp;quot;, so I&amp;#x27;m sure I&amp;#x27;m missing a piece. Is it only PR that underline this aspect? Is JWST as brittle as the news want to make us think? Or are there technical reasons or acceptable failure modes that gives confidence that those steps are not as critical as the news let us people know?</text></item></parent_chain><comment><author>lamontcg</author><text>JWST is driven by the size of the mirror, the need for an IR instrument and the temperature you need to keep the instrument at to do the observations.  Spamming a bunch of hubble-sized instruments up into orbit won&amp;#x27;t accomplish the same thing.  And I don&amp;#x27;t think you can do space VLBI in the optical&amp;#x2F;IR or it would have been done already (but I don&amp;#x27;t know why?).&lt;p&gt;It is kind of like asking why 5 Ford Rangers can&amp;#x27;t replace one Lamborghini or something.</text></comment>