You raise some good points here; namely, that there are political considerations beyond just congressional funding. If your flagship mission is supposed to be a collaboration with the ESA, then changing launchers away from the Ariane 5 is probably not in the cards. Also, missions that are scientifically useful but don’t produce “pretty pictures” are hard to justify to the public.
One impression I get from notes on the early days of the JWST/NGST is that Dan Goldin and others pushed people to think big. Some thought that a 4-meter scope would be a very reasonable upgrade over Hubble. But… why not push for more, say 8m or 10m? There’s little reason not to, and you can always compromise your way to something slightly more modest. It takes a slight suspension of disbelief to pretend that an 8m scope can be done for the same cost as a 4m scope, but you can always repeat some mantra like “faster, better, cheaper” or “next-generation technologies” and handwave that away. Maybe you don’t actually believe it can be done for the price you’re saying, but that’s a problem for years down the road.
Everybody is bad at estimating costs on an emergent technology that is beyond current experience. The point of doing so is to push the edge of the envelope of what is possible. NASA could have put another Hubble-type spacecraft in Low Earth Orbit with a near-infrared sensor instead of visual range, but then it wouldn’t be a Next Generation Space Telescope.
You’re acting like there’s no middle ground between a Hubble v1.1 and the JWST. A 4m far-infrared scope at L2 without the super-intricate folding mirror and a less complex sunshield would have still been an amazing instrument, and probably wouldn’t have eaten the budget of projects like the Terrestrial Planet Finder.
Earlier I suggested that demo missions should have been flown to prove out some of the basic technologies of the JWST. I said that just because it’s obvious to me, but found a blurb hinting that NASA thought the same and had planned out some missions. I found some cites for one such mission:
Design and Flight Testing of an Inflatable Sunshield for the NGST
The Next Generation Space Telescope (NGST) mission is scheduled to launch in 2007 and be stationed at L2 for a mission life of ten years. The large aperture mirror and optical detectors aboard NGST require shielding from the constant solar energy seen at this orbit. The government reference NGST design, called the Yardstick, baselined a sunshield using an inflation deployment system. During the formulation phase, NGST is spending approximately 25% of the overall budget to foster the development of new technology. The goal is to develop and demonstrate enabling or enhancing technology and provide innovative solutions for the design of the NGST observatory. Inflatable technology falls in the category of enhancing technology due to its advantages in weight, stowed volume and cost. The Inflatable Sunshield in Space (ISIS) flight experiment will provide a realistic space flight demonstration of an inflatable sunshield.
“ISIS” is a bit of an unfortunate name for the mission. I can’t find why it was cancelled, but it seemed tied to the Space Shuttle. The Columbia disaster would have probably done it in, but it seems like it was cancelled before that point.
Reinhard Genzel of Germany’s Max Planck Institute for Extraterrestrial Physics in Garching says it was clear at the time that a $500-million estimate for the Webb telescope was a “political price”. Yet such was the climate of the 1990s that when estimates for the European Space Agency’s smaller Herschel infrared observatory came in at $1 billion, he says, “I was approached by many colleagues saying, ‘You guys are so stupid. Why can’t you do this for less?’ That’s now haunting NASA, of course.”
Today, Illingworth inveighs against the “extraordinarily bad, artificial cost estimates” of the Goldin era. But the 2000 Decadal Survey seems to have been happy to accept them. The world of big science is well used to projects being lowballed — a process that gets schemes started on the basis of a low cost estimate, with the implicit hope that by the time the true costs are known inertia and vested interests will make it impossible to pull out. Lowballing is not a practice anyone would defend on principle, but histories like the Hubble’s show it can work (see page 127).
Assuming you believe them, the $500M was an intentional lowball. And yet it was believed by some. Lowballing wouldn’t work unless you convince someone.
NGST/JWST was absolutely “supposed” to be a 9-figure project, even if the people involved didn’t really believe that number. That’s how the project was sold.
Just for completeness, today saw the release of nicely processed pretty images of Jupiter from the JWST. It took a bit longer than I thought it might. But nice stuff. Certainly rival the HST’s visible light images.
One thing to remember is that Jupiter is moving fairly fast.
That big red spot/storm only takes about 5 hours to move across the planet.
Any exposure longer than a few minutes is going to be blurred.
Read this gifted NYT opinion piece How the Webb Telescope Expanded My Universe where the author says “The latest images, released Monday, hit closer to home.” It’s a nice tribute to how Webb (and other images) are revolutionary.
In principle I think the answer is yes. With some back of the envelope calculations the image is about 10 pixels per degree of longitude in the centre of the image. The planet rotates about half a degree per minute, or five pixels a minute. So you are looking at only say five seconds exposure to avoid blur, at least in the middle of the disk.
At the JWST, Jupiter sits between 30 and 50 arc-seconds in diameter. NIRcam gets 0.031 arc-seconds per pixel. So up to about 1000 to 1500 pixels across (which close to what the images we have are.) So in order to track a feature the JWST would need to slew at up to about 0.15 arc-seconds a minute.
The JWST is gyro stabilised and tracks using the gyros as reaction wheels. Whilst it points steadily into space, in reality it is always actively station keeping and maintaining pointing. There is no reason it could not be slewing at a tiny rate, however whether the control systems are capable of doing so is another matter. They like to lock onto a guide star rather than run open loop. I wonder if the guidance system could be run in a manner that deliberately ran the guide star across the sensor at a known rate. The fine guidance sensors only have a resolution of 0.069 arc-seconds. But they are 2000 pixels across, so it isn’t impossible they could manage to set up and control a known slew rate relative to a target. Who knows what amusing tricks the system has.
(I’m ignoring the apparent motion of the the planet here anyway.)
