Quote from: Robotbeat on 06/30/2013 05:03 pmthe House is trying to cut all funding.There is no extant funding for this which they could "cut." Some in the House are trying to prevent the creation of any funding.
the House is trying to cut all funding.
ChileVerde: your quote needs context. NASA is currently looking at two specific asteroids for the retrieval mission (though there are many other possibilities), and the best-understood earlier target (for which we have decent mass and spin-rate figures) can't be done unless stakeholders agree to it. The second target has been characterized less thoroughly right now.
Looks like they originally estimated the solar arrays, engines, and structure at 5000 kg ... when they realized they had another 995 kg available from the Atlas, they decided to use it. Sounds reasonable to me.
Does any one have an estimate on how much Xenon costs per KG?
About $1200. Google is your friend, if you use it. 12,000 kg X $1200 / kg is $14.4 million. Fuel (or in this case, reaction mass) is cheap compared to the other costs of a space mission. Still, using Argon would save a few million dollars. At $5.00 per kg, 12,000 kg of Ar comes in at $60,000.
Xenon works.All about the TRL.You'd spend that $14.4 mill in a couple of weeks trying to catch up in development with other propellants.
And there are ways to reduce Xenon's cost if it came down to that.
[rant]Please note that the names of chemical elements, e.g., xenon and argon, are not capitalised.[/rant]
{snip}The asteroid retrieval mission is either going to be using an array of gridded ion thrusters (such as NEXT, which has a rather high TRL and really, really good total efficiency--not to mention long demonstrated total life--but also probably too high of an Isp, a problem which would get much worse if you used Argon or Krypton, plus the efficiency would be lower and dry mass higher) or Hall thrusters (i.e. the 20kW units from JIMO, also being tested as we speak). And both would use Xenon.
Quote from: MP99 on 06/06/2013 06:35 amI don't see this happening before 2025, by which time we may already have done em-2 thru em-5. And speaking of that, I just noticed the following:Quotehttp://science.nasa.gov/media/medialibrary/2013/06/21/Minutes-NAC_Science_April_18-19-130620b-SIGNED.pdfNASA Advisory Council Science Committee Meeting, April 18-19, 2013<much snippage>Mr. Gerstenmaier reviewed the interplanetary trajectory of the planned mission; 12 metric tons of xenon (Hall thruster) will be used to test its capability in terms of duration and impulse. Reaching the object will take 1.84 years and the traverse back to Earth 2.99 years.<snip>Responding to a suggestion to use a 2021 cruise mission for the mission, Mr. Gerstenmaier commented that the object cannot be obtained any sooner than 2024. However, HEOMD should be ready to launch to it by 2021. There is a calendar disconnect - this is a feasibility study only, not a mission design.<much more snippage>Now, these notes are distressingly gnomic, but I'd tentatively interpret them to mean that the Orion-asteroid rendezvous won't happen until 2024 at the earliest. As the present SLS launch schedule has EM-2 in 2021, EM-3 in 2023 and EM-4 in 2025, it would appear that EM-2, even though "ready" to go to the asteroid, won't have an asteroid to go to. Possibly the same for EM-3, though it might be delayed if an asteroid were indeed on the way. So what are EM-2 and possibly EM-3 to do? I'd guess trips to DRO to practice for an actual asteroid rendezvous.P.S.: Another implication is that the SEP asteroid-grabber probably won't launch before 2020, which seems reasonable.
I don't see this happening before 2025, by which time we may already have done em-2 thru em-5.
http://science.nasa.gov/media/medialibrary/2013/06/21/Minutes-NAC_Science_April_18-19-130620b-SIGNED.pdfNASA Advisory Council Science Committee Meeting, April 18-19, 2013<much snippage>Mr. Gerstenmaier reviewed the interplanetary trajectory of the planned mission; 12 metric tons of xenon (Hall thruster) will be used to test its capability in terms of duration and impulse. Reaching the object will take 1.84 years and the traverse back to Earth 2.99 years.<snip>Responding to a suggestion to use a 2021 cruise mission for the mission, Mr. Gerstenmaier commented that the object cannot be obtained any sooner than 2024. However, HEOMD should be ready to launch to it by 2021. There is a calendar disconnect - this is a feasibility study only, not a mission design.<much more snippage>
QuoteAnd there are ways to reduce Xenon's cost if it came down to that.Could you elaborate on those ways? Xenon is exceedingly rare.Just to be clear, I do not see a cost problem using Xenon in a one-off asteroid capture mission, or for one-off missions to the outer planets, for example. But if someone ever starts to reuse these tugs commercially to capture asteroids then the cost of the Xenon fuel counts. After all it costs more than 10% of the launch costs of the fuel launched for refueling the tug in LEO. (Say that launch vehicle costs $70 M, so the Xenon fuel payload is then 20% of the cost to refuel the tug in LEO.) That number becomes significant compared to the cost of bringing the TRL of other engines/fuels up to 8 - 10, in a reusable environment. And don't throw out the ISRU argument, that solution will cost way more and commercial enterprises will not pay for it until they are profitable and ISRU is proven.