Personally I hate launching anything around the Christmas period.
Webb flies Ariane 5: watch the launch live on 25 December
161–170 of 188 posts
Re: Webb flies Ariane 5: watch the launch live on 25 December
#162Earlier quoted context omitted.
I suggest the book "Failure is not an option" 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. I don't think that a raw metric of the number of SPOF is the right way to measure the risk of this spacec…
What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…
There are many people in NASA and around that have made similar arguments.
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.
Re: Webb flies Ariane 5: watch the launch live on 25 December
#163Earlier quoted context omitted.
I suspect the deployed structure cannot handle the acceleration required for escape velocity. That also may require much more propellant. Then on top of that, we don’t have the capability for humans to service satellites other than the ISS. So this is all a moot point.
What about an unmanned mission to fix it? And maybe to refuel it.
Incredibly unlikely. First, it would have to fail in a way that’s possible to fix. We don’t have robots that can replace screws, solder joints, and polish mirrors in space. Then we’d have to design a brand new spacecraft and mission. That would take years, lots of money, and political will. NASA would likely cut its losses, document the lessons learned, and try again.
Re: Webb flies Ariane 5: watch the launch live on 25 December
#164Earlier quoted context omitted.
What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…
There are many people in NASA and around that have made similar arguments. 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.
Yeah when you have a fickle funding source often the only way to get any long-term project done is to make it too big to fail, but then you see all the other terrible waste, corruption, etc. that accompanies that.
Re: Webb flies Ariane 5: watch the launch live on 25 December
#165Earlier quoted context omitted.
What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…
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't accomplish the same thing. And I don't think you can do space VLBI in the optical/IR or it would have been done already (but I don't know why?). It is kind of like asking why 5 Ford Rangers can't replace…
Spamming a bunch of hubble-sized instruments up into orbit won't accomplish the same thing.
It will, and then some, once we get optical interferometry nailed down. JWST is great, and needed to be done, and I'm glad it's finally getting deployed. But if I had an argument to make against it, it would be, "Let's wait until we know how to do this properly. We're not there yet."
That's a weak argument and should almost never be heeded, but it's also not wrong.
Re: Webb flies Ariane 5: watch the launch live on 25 December
#166Personally I hate launching anything around the Christmas period.
LaunchHN: JWST on Christmas
Re: Webb flies Ariane 5: watch the launch live on 25 December
#167Earlier quoted context omitted.
I suspect the deployed structure cannot handle the acceleration required for escape velocity. That also may require much more propellant. Then on top of that, we don’t have the capability for humans to service satellites other than the ISS. So this is all a moot point.
What about an unmanned mission to fix it? And maybe to refuel it.
But who repairs the repairers?
Re: Webb flies Ariane 5: watch the launch live on 25 December
#168We're told that since JWT will travel very far away before it unfolds and activates all its systems, there is no practical way to service it if something would go wrong. Why can't it unfold etc in Earth orbit, where a repair mission can be sent if needed, and then travel to its Lagrange point?
It's a problem of energy and orbits. To get from low-earth orbit to the sun-earth Lagrange point 2 (where the JWT is headed) takes around 7 km/s of delta-v[0]. That's a lot of speed. You could try to do this gently enough that the unfurled JWT won't be damaged by the acceleration. This isn't totally impossible, but you'd need a good Hall thruster (ion engine) with a huge amount of reaction mass, since the JWT is so b…
[deleted]
Re: Webb flies Ariane 5: watch the launch live on 25 December
#169Earlier quoted context omitted.
I suggest the book "Failure is not an option" 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. I don't think that a raw metric of the number of SPOF is the right way to measure the risk of this spacec…
What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…
I think this is because of how the various constraints work against each other. We need the telescope to be as large as possible to work as well as possible. But the rockets can only be so big (i.e. we're constrained by the largest available booster). The only thing here under our control is how hard we work on fitting the biggest possible instrument in the available payload envelope, and that is exactly what happened.
With a machine this complex I think it's also not easy to crank out multiple copies since I'm imagining most of it is made by hand without the benefit of a production line.
Re: Webb flies Ariane 5: watch the launch live on 25 December
#170Earlier quoted context omitted.
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't accomplish the same thing. And I don't think you can do space VLBI in the optical/IR or it would have been done already (but I don't know why?). It is kind of like asking why 5 Ford Rangers can't replace…
Spamming a bunch of hubble-sized instruments up into orbit won't accomplish the same thing. It will, and then some, once we get optical interferometry nailed down. JWST is great, and needed to be done, and I'm glad it's finally getting deployed. But if I had an argument to make against it, it would be, "Let's wait until we know how to do this properly. We're not there yet." That's a weak argument and should almost ne…
The reason we can't achieve the same resolution as JWST with interferometry has been mentioned in a recent startalk podcast. The distance between the telescopes would have to be coordinated to a precision somewhere on the order of nanometers.