This is a fundamental problem with our funding approach - if you price something at what it's going to cost, it'll never get funded. If you price it to get funded, you're going to get criticized - or cut - when it ends up costing what it actually costs.
There's much in common between this discussion, and the decadal survey discussion, and the "what to replace SLS with if it's cancelled" discussion.There's the old saying that you never want to see sausage being made, or political decisions being made. These funding decisions are irreducibly political, since they have to be made by politicians. So low-balling prices gets you in the door, sunk cost keeps you going, and then you end up on the plate with eggs and potatoes. It's ugly, from a strictly "pure" perspective, but not much that happens in political situations (or between even well-meaning people) is pure. There are almost always compromises and bending of rules.
"Never ascribe to malice..." comes to mind during this discussion.
I skipped that thread because I figure that it's a lot of the typical flailing of arms and opinions masquerading as facts (I bet "Falcon Heavy and Red Dragon will get us to Mars!" is a common theme).
Talked to somebody knowledgeable.Yeah, they are using the NRO optics (they were not given all the optics). They have to build a lot of stuff to get it up to spec, because it was not designed to astronomy spec.Using the optics loses some of the farther IR stuff because the optics cannot get too cold. However, compared to the earlier WFIRST concept, this one can do much more exoplanets stuff. So they lose things but gain things and whether this is good or bad depends upon which bit of science you want to do. Some people are very unhappy, the exoplanets people are happy.The tough issue is cost. This is going to cost a lot more than originally planned. I think that the original plan was to do it at around $1.8 billion in FY15 dollars. The actual price is going to be significantly more than that (although probably not twice as much). Those numbers may already be public, but if not, they soon will be. What I don't know is if the NRO optics actually saved any money. Maybe if they had started from scratch they could have kept the cost lower. We'll have to wait a decade or more for somebody to write a paper about that.
3. The telescope is warm (we’re looking at around 284 K), but remember that the infrared science program that was selected for WFIRST by the Decadal Survey goes out to a wavelength of 2 microns. Thermal emission is determined by the Wien part of a blackbody curve, multiplied by the net emissivity of the mirrors, and with margin tacked on; that depends very strongly on both wavelength and temperature, but basically it is less than the sky background from the zodiacal light at wavelengths up to ~1.76 microns (exact number depends on where you look) and rises rapidly thereafter. In the reddest wavelength filter used for imaging on WFIRST (still being discussed, but roughly 1.7-2.0 microns) it works out that the sensitivity of the warm 2.4 m telescope is about the same as a cold 1.5 m telescope (what was recommended in the Decadal Survey). If you went farther into the infrared, the colder, smaller telescope would be better, but for most of the planned science program the 2.4 m is a big win.[3B. The coronagraph uses silicon detectors sensitive to ~1 micron and so the thermal emission isn’t an issue there. The wide-field near infrared camera is affected by the telescope emission, and the optical design actually re-images the primary mirror and has a mask to block the thermal emission from the baffles and secondary support struts, which are much more emissive than the silver coating on the telescope mirrors. This is a common procedure in astronomical IR instrumentation. Note that the 3-mirror optical design gives you a natural place in the instrument to do this.]4. The telescope points into empty space and needs heaters to maintain it at the operating temperature. The detectors, on the other hand, really do need to be cold (in the range of 90-100 K) to suppress dark current. They will be actively cooled with a closed-loop (no consumables) mechanical cryocooler.6. Some modifications to the telescope are needed (discussed in the SDT report referenced earlier in this thread). To make a corrected wide-field reflecting telescope you need at least 3 powered mirrors, we are given 2 (these will have some modifications) and the 3rd is new (located in the wide-field instrument).
NASA funded the develpment sensor for NEOCam (which apparently is called "the NEOCam sensor") as part of the Discovery #12 selection. The sensor is supposed to perform infrared observations with a warmer mirror:https://www.nasa.gov/mission_pages/asteroids/multimedia/pia16955.htmlhttp://neocam.ipac.caltech.edu/news/tracking-sensor-passes-testhttp://www.spacesafetymagazine.com/space-hazards/asteroid-hitting-earth/nasas-asteroid-tracking-sensor-green-test/ Could some kind of enlarged version help WFIRST-AFTA with Far Infrared observations?
AFAIK the main novelty of the NEOCam sensor is that the sensor itself doesn't need to be as cold as with current techniques, so less cooling (or even completely passive cooling) would be enough. With WFIRST the problem is that the whole telescope is so warm that its own emission drowns the signal from astrophysical objects.
Quote from: as58 on 01/17/2017 09:20 PMAFAIK the main novelty of the NEOCam sensor is that the sensor itself doesn't need to be as cold as with current techniques, so less cooling (or even completely passive cooling) would be enough. With WFIRST the problem is that the whole telescope is so warm that its own emission drowns the signal from astrophysical objects.Aren't they also looking at different wavelengths?
If everybody in Congress took into account "the sunk cost fallacy" and simply canceled stuff when it got expensive, then nothing would ever get built.
Sad news related to the mission: Neil Gehrels, WIRST project scientist and the PI of Swift mission died yesterday.
NASA is currently looking at ULA’s Delta 4-Heavy or SpaceX’s Falcon Heavy rocket to send WFIRST into space, according to Dominic Bedford, the mission’s program scientist at NASA Headquarters.
NASA officials want to keep WFIRST’s total cost around $3.2 billion — in current-year economic conditions — and Bedford said the space agency could “descope” the mission by removing the coronagraph instrument if it looks like it will bust the budget cap.“The coronagraph is not required for mission success, so we can back off the coronagraph if necessary,” Bedford said in the April 13 meeting of the NASA science advisory committee.Multiple internal and external cost assessments will be completed in the coming months to inform NASA decision-makers on whether WFIRST should remain intact.An cost assessment by the Aerospace Corp. in 2015 put WFIRST’s project cost between $2 billion and $2.3 billion. A report issued by the National Academy of Sciences last year said the cost of WFIRST had increased by $550 million since the Aerospace Corp. study, and the review panel recommended NASA slash the observatory’s capabilities, such as removing the coronagraph, if costs continued to grow.
“Budget is a big concern,” Bedford said. “The concern I’m mostly recognizing now is the overall mission cost of $3.2 billion. We have to make sure that we make the right choices to keep the science capability while keeping under that cost.“The problem with mission design is you tend to have a function of science vs. cost that is steep,” Bedford said. “You lose more science than you lose cost.”
More photos of the mirror are available at https://wfirst.gsfc.nasa.gov/gallery-photos.html. I wonder how the price tag has gone from $2.6B- $2.8B given in last year's decadal mid-term to $3.2B. It's not quite clear if both estimates include the same things, though. Slides from last week's NAC Science Committee meeting don't seem to be available yet.
Quote from: as58 on 04/21/2017 10:40 AMMore photos of the mirror are available at https://wfirst.gsfc.nasa.gov/gallery-photos.html. I wonder how the price tag has gone from $2.6B- $2.8B given in last year's decadal mid-term to $3.2B. It's not quite clear if both estimates include the same things, though. Slides from last week's NAC Science Committee meeting don't seem to be available yet.Isn't it the addition of the Coronagraph pushing the price tag up?