10 ms·
NASA Says Webb’s Excess Fuel Likely to Extend Its Lifetime Expectations
- Sharlin 5y agoBig props to Ariane 5 and the whole Arianespace team for executing such a precise insertion.
- asplake 5y agoTempting fate perhaps even to ask, but I wonder if an unmanned refuelling mission might be possible?
- jstrodd 5y agoThere is a very good and detailed answer to your question here: https://space.stackexchange.com/questions/38389/is-it-possible-to-refuel-the-james-webb-space-telescope https://space.stackexchange.com/questions/38389/is-it-possib...
- bryanlarsen 5y agoThat's a very good answer. A few more points, because the answer is a 2.5 years old. - the docking adapter discussed in the answer did not make it. However, the answer offers a couple of alternatives, so +1. - they painted some crosses on the JWST to make alignment easier. - JWST's L2 location is really far from Earth. It's about 4X the distance from the moon. So a manned mission is currently infeasible. But maybe in the future. - while fueling may be possible, any other sort of maintenance probably isn't. To save weight, the JWST is mostly glued together, unlike Hubble which used spacesuit accessible bolts.
- zackbloom 5y agoIt's also worth noting that much of JWST is now twenty year old technology. Assuming it isn't a total failure which needs to be salvaged for PR reasons, it will almost certainly make more sense to build a new observatory in ten years rather than rescuing this one. If Starship exists at that point it will also be a much less complex undertaking to get it into space, and it could likely use an even bigger mirror.
- vlovich123 5y agoThe complexity of the undertaking was not building the rocket. The complexity is the telescope itself. It would be interesting what the costs come down to if rather than starting from scratch they iterated on existing designs. Anyone know what the incremental cost of building the same telescope again would look like?
- pirate787 5y agoMy understanding is that a lot of the complexity is making the telescope able to fit in limited space and then unfurl. That constraint is lifted significantly with Starship.
- wolfd 5y agoI think that the other commenter was referring to the relative complexity in JWST's unfolding/deployment. It might be possible to deploy something from Starship that doesn't need to be packed as tightly (and save on engineering costs there) and still get around the same performance. A complicated sunshield deployment seems somewhat inevitable, personally, but I'd be happy to be proven wrong there.
- yupper32 5y ago> So a manned mission is currently infeasible. But maybe in the future. Given the increased interest in manned missions and recent technology advancements/investments, I wouldn't be surprised if we could get there in 15-20 years, which sounds likely to be when it'd need to be refueled. If it's worth it or too dangerous to send an astronaut to deal with the dangerous refueling operation are whole other questions. But actually getting there? I think we can do it in 15-20 years.
- tekno45 5y agoThey are planning one!
- Tepix 5y agoSource?
- Arubis 5y agoPhysics doesn’t make this impossible, but it’s _enormously_ expensive to get payload to L2.
- toomuchtodo 5y agoI am not familiar with the station keeping needed for maintaining an L2 orbit; would it be possible to use an Earth orbiting laser to apply photonic force against JWST's solar shield (turning it into a laser sail) to balance it "falling back" towards Earth without onboard propellant? My understanding is that it has a gravitational weighting towards Earth to prevent slipping away.
- vikingerik 5y agoIs it enormously expensive because of physics or because of bureaucracy and politics? Like, serious question: how much cost are the raw materials for the fuel and spacecraft/rocket, and how much are the costs like human labor and ground transportation to the launch site?
- nabla9 5y agoHershel operated 4 years and one month, but this was because it needed liquid helium coolant and it eventually ran out. Hershel was planned to operate 3.5 years. btw. Hershel wast the first optical telescope placed in L2. It was also it was also the largest optical space telescope before JWST.
- julienchastang 5y ago"though many factors could ultimately affect Webb’s duration of operation." JWST also needs helium coolant with no possibility to recharge therefore limiting its lifespan to ~10 years, I believe. Interesting about Herschel and L2.
- bryanlarsen 5y agoIIRC, the helium coolant is only used on one of JWST's 4 instruments. So if they run out of helium the other three can still be used.
- terramex 5y agoIt does use helium only as refrigeration fluid in closed cycle, it does not get depleted. Building a cryocooler capable of achieving so low temperatures without boiling helium off was a major hurdle in JWST development.
- vlovich123 5y agoIsn’t helium notoriously hard to contain without leakage even in a closed system?
- dnautics 5y agothat's hydrogen. IIRC from my chemistry days, Helium is hard to contain in plastic closed systems, but "generally OK" in metal tubing.
- 5y ago
- Maxburn 5y agoSee where Webb is on the way to L2 orbit; https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html Fun to see where it is on deployment. It's also interesting to me that the mirror appears to be fully exposed to space unlike Hubbell. If anyone knows something about that design choice I've like to hear it.
- wmf 5y agoIf the optical path was enclosed the JWST would probably be too big to fit on any existing rocket.
- Laremere 5y agoFactors I can think of: 1. Bigger mirror = better. Enclosing a mirror requires mass and volume, limiting mirror size. 2. The L2 orbit is unstable. Far less risk of being hit by debris than low Earth orbit. 3. Webb's sun shield blocks the primary light pollution angle. Hubble would need more protection from all angles due to the Sun, Earth, and Moon.
- anonAndOn 5y ago4. Any variations in temperature in the mirror array affect geometry/optics
- Maxburn 5y agoI was just reading that after L2 insertion it's going to take five months to get everything cooled off and aligned properly. Amazing.
- jacquesm 5y agoCooldown has already started with the deploying of the sunshield from it's launch position, even before it is unfolded fully and stacked properly the delta is already a whopping 60 degrees Celsius across a bit over two meters.
- 5y ago
- yeetaccount4 5y agoNASA likes to pull the old mechanic’s trick of underpromising and over delivering.
- bryanlarsen 5y agoThat's just a natural consequence of designing with safety margins. In other words, it should be the norm and not the exception. But of course the vast majority of us work in fields where overpromising is the norm.
- vikingerik 5y agoAnd think about how many layers of safety margins. If there are ten subsystems each with a 20% safety margin to say that their designers did their jobs right, then you might have an overall system with as much as 200% safety margin. (yeah not everything is linear like that, but illustrating the point.)
- beckingz 5y agoIt's career ending to not do that.
- Salgat 5y agoIt's so consistently done by NASA that I'm no longer impressed when they reach past EOL. It just shows that they were covering their asses.
- mrfusion 5y agoI never understood how we launch to earth sun langrange points? By starting from earth we’re already at the correct orbital velocity around the sun so do we just cruise out there and cancel out the delta v we used to get there?
- mabbo 5y agoRemember that no matter how far from the earth you get, you're always being pulled by it, decreasing velocity. The Webb left earth moving at 7km/s, but now is going less than 1km/s. It's going to let Earth's gravity slow it down so that it reaches (effectively) zero at exactly the right spot. It's literally rocket science to do the equations to make it work, but by God we've gotten pretty good at it.
- kibwen 5y agoTake a look at the dashboard and note the current speed: https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html Right now it's traveling at about 0.55 miles per second. When I checked the other day that was over 0.7, and a bit after launch it was over 1. Putting JWST into L2 is essentially the world's biggest curling toss ( https://en.m.wikipedia.org/wiki/Curling https://en.m.wikipedia.org/wiki/Curling ). As the OP alludes to, JWST's operational life is hard-limited by its fuel capacity. L2 (like L1 and L3, but unlike L4 and L5) is an unstable orbit, and without regular corrections it will drift out of position. This means that you want to save ALL your fuel for making those corrections, and thus spend as little of it as possible on getting there in the first place. So over the next month it's going to slowly crawl into place, cruising on no power other than what the Ariane initially gave it, getting continually slower and slower via the effect of the earth and sun's gravity until it stops perfectly in position.
- blackoil 5y agoCan anyone with knowledge provide a rough estimate of how much would it cost to manufacture a second telescope considering all the research cost is assigned to first one. It is a hypothetical question to understand if we had lost it in launch would it have been a complete loss or can we have 2nd one within couple of billions and 3 years.
- idealmedtech 5y agoA lot of the core research wouldn't have to be repeated, but the build and verification costs would not go away, and to do proper verification takes many many years.
- bryanlarsen 5y agoA lot of those people hang out in the comments on Eric Berger's posts on Ars. Here's one example: https://arstechnica.com/science/2021/11/james-webb-space-telescope-cleared-for-late-december-launch/?comments=1&post=40442499 https://arstechnica.com/science/2021/11/james-webb-space-tel... He estimates that a second would cost about 90% of the first.
- pas 5y agoSo what's next? Modular telescopes? Couldn't the whole manufacturing of the module (semi-)automated? (So no need for so much testing, verification, etc.) Bring unit costs down, and launch a few of the modules each year. Eventually they'll have as big a mirror as they want.
- miohtama 5y agoA telescope that is assembled in space.
- nullc 5y agoI suspect it wouldn't be easy to incrementally build up a single large aperture because the secondary optics needed would be different at each size. If we build telescopes for optical vlbi we could build a fleet to have the resolution of a telescope kilometers across... I believe VLBI has been accomplished experimentally at MWIR wavelengths.
- jacquesm 5y agoThat propellant tank is massive.
- wolverine876 5y agoNASA may be the greatest engineering organization in human history; I can't think of any competitors. They are also masters at consulting: Underpromise, overdeliver. 'The rover is planned to last one year.' 'Amazingly, it is still working after three years!'
- quesera 5y agoJust to enumerate some recent missions: * NASA Curiosity: "2 years" -> 9.5 years, and counting. * NASA Spirit: "90 days" -> Just over 6 years, ending in 2010. * NASA Opportunity: "90 days" -> Over 14 years, ending in 2018. NASA has had some failures too, of course. These stats are cherry-picked but still impressive.
- wolverine876 5y agoMy point is that it's not impressive, it's just an old sales technique. Curiosity could have been designed for 20 years, but all NASA needs to do is say '2 years' and the project sounds like a resounding success if it fails in 10. (It is extremely impressive to have rovers and helicopters traversing Mars.)
- Rebelgecko 5y agoIt's pretty much expected, these sorts of complex systems follow a bathtub curve. Failures either happen very early or after a very long time. If you design something so that it has a 99% of lasting 1 year, there's pretty good odds that it'll make it to 5 years since the riskiest time is the first weeks/months.
- quesera 5y agoThat's a cynical perspective. though. In each of the above cases, the mission end date was extended because the hardware was capable of doing more science (or for more time) than it was designed for (and budgeted for). Like JWST, some of the procedures required for a successful mission had never been done before, and could not be tested fully on Earth. Many of those procedures have implications on mission longevity. Very smart and dedicated people make their most educated guesses, build in what they know, try to handle the unknowns, and hope and pray -- and more often than not, are proven correct. That's pretty close to my personal definition of "impressive engineering". There's a political angle too, of course. We don't know what NASA's "estimate fudge factor" is. I'd be amazed to learn that it is 5x, 24x, or 56x.
- zeristor 5y agoA key thing is that several years ago they realised that the reaction wheels were failing earlier than planned, some nifty deep analysis found the issue and I hope that this means they’ll last long enough. The Reaction wheels are used to rotate the space craft without the use of fuel, and Scott Manly, as ever did a great video on this: https://youtu.be/KibT-PEMHUU https://youtu.be/KibT-PEMHUU
- nullc 5y agoI wonder if Webb having a longer life won't be bad for us in the long run. Webb was designed a long time ago, with tech that is now pretty old. It's a design that was heavily compromised by the limits on what we could lift into space at the time. It seems likely to me that in ten years time we could build and lift a much better instrument. But if Webb is still working will we have the political will to do so? By then low hanging science that could be done with this instrument will probably be done (or they would have engineered it for more than 5 years...). There are plenty of older prestige instruments that no longer get used for much important science because it is career suicide to invest your time on an instrument where other people have already found all of the easy and medium difficulty discoveries reachable from it. (e.g. as was the case for arecebo before it collapsed) It's not hard for me to imagine that ten or fifteen years from now Webb isn't being very effectively used because the scientists attention are elsewhere and where we could build a vastly superior instrument, but we don't because webb still works. Maybe someone more aware of the realpolitik of astronomy projects will tell me that I'm being pessimistic for no good reason. :)