Quote from: kraisee on 06/25/2009 07:24 pmEven with the mitigation efforts, TO on Ares-I is expected to still be able to impart up to +/- 2.0g of vibrations on the Crew Module, although seat isolators are hoped to reduce that for the crew themselves.Ross.At those kind of alternating loads you have to start looking at Metal fatigue.. not just Ultimate and Tensile strength. I would want a higher FS for material in that envirnoment.
Even with the mitigation efforts, TO on Ares-I is expected to still be able to impart up to +/- 2.0g of vibrations on the Crew Module, although seat isolators are hoped to reduce that for the crew themselves.Ross.
I like your DIRECT approach, but there is one major problem. The manned Mars mission is still in the too-distant future (2032 or something).Everything MUST be done in order to chop at least 10 years from the current DIRECT proposal. Please, look at this thread.
Lets just say that they have been asking questions, we are preparing data for them and some of the team have made contact directly. And the contacts have all been good so far.
Quote from: William Barton on 06/25/2009 09:30 pmYou'd never manage a Mars landing by 2022, but you might manage Phobos. (Or some such data, I haven't looked at the potential launch windows.)But what if VASIMR works well? In theory it can reduce the one-way trip time to 30 days.One month to Mars, one month on Mars, and one month to Earth. That's only three months! Doesn't sound too risky anymore.
You'd never manage a Mars landing by 2022, but you might manage Phobos. (Or some such data, I haven't looked at the potential launch windows.)
{snip}I can understand EML1, as you are between the Earth and Moon. For L2R, you'd need to be on the far side of the moon? Wouldn't that burn extra fuel to get there than L1R?
Why did Apollo take the CSM and LEM to LOI?{snip}
It's possible that a succession of non-lunar-landing missions, done at about one year intervals, might excite the public interest in (and willingness to pay for) a Mars landing, which would speed things up. Say, a lunar orbital mission (view or nearby Moon), a visit to Webb (view of Earth from much farther than the Moon), a visit to a "nearby" NEO (round trip of a few weeks), then a visit to a more "remote" NEO (round trip of a few months), finally a trip to Phobos. None of that would require the massive investment a Mars landing would require. And the view of Mars from Phobos must be staggering. You'd never manage a Mars landing by 2022, but you might manage Phobos. (Or some such data, I haven't looked at the potential launch windows.)
The most critical factor in any 2-launch Lunar mission architecture is maximizing the amount of propellant lofted to LEO for the TLI. Anything which might reduce that capacity, reduces Lunar performance by a factor of more than 3, so if you lose just 300kg of TLI propellant to LEO, the effect is actually that you lose about 1 full ton of payload performance actually being sent to the moon.
It's theoretically possible. It's a 7.3mT PLF so that's a significant weight penalty which will increase the propellant needed to do the burn.
Quote from: kraisee on 06/24/2009 09:40 pmThe most critical factor in any 2-launch Lunar mission architecture is maximizing the amount of propellant lofted to LEO for the TLI. Anything which might reduce that capacity, reduces Lunar performance by a factor of more than 3, so if you lose just 300kg of TLI propellant to LEO, the effect is actually that you lose about 1 full ton of payload performance actually being sent to the moon.The factor of three is incorrect. I reported this error in my Direct Rebuttal review. Here is what I wrote."p.71 Direct claim that for every kg of EDS stage mass increase, this results in 3 kg loss in payload mass through TLI. This is incorrect. You first lose 1 kg of payload mass due to EDS stage mass increase. You then lose 0.93 kg by not having the extra 1 kg of propellant available. Total payload loss is 1.93 kg, 35% less than what Direct claim.
For Altair mp = 45.0*(exp(55/4167.-1) = 598 kg
But the burnout mass of the EDS through TLI is also increased by 1 kg, which consumes an additional 1.07 kg of fuel which is unavailable for injecting payload.1.93 + 1.07 = 3.0 kg reduction.
You can also just tick the "don't use smileys" tickbox.
Taking some snippets from http://www.spaceref.com/news/viewsr.html?pid=31601 titled "NASA ESMD Internal Memo from Jeff Hanley: 6/20 Cx Update - Moving Forward".QuoteMuch attention has been focused on the probability of loss of crew (pLOC) as a figure of merit in determining the crew launch aspect of the architecture, and we expressed that the ESAS pLOC numbers were all using the same methodology and that the value was in the comparative results and not in the absolute numbers. Very simply, Ares' clear advantage is in the comparative simplicity of its first stage (the shuttle SRM) and use of a single gas generator cycle upper stage engine. These two attributes alone provide substantial robustness over, for example, a more complex liquid pump fed first stage and a multiengine upper stage - simply put, they are more complex with more moving parts. What Ares affords us, in accordance with the findings of the CAIB, is a crew launch system that has the potential to achieve unmatched safety in human spaceflight history. And this is not just a Constellation 'claim' as some would suggest, but has been validated by independent experts in the field of physics based probabilistic risk assessment. There will be much more provided on this topic as well.
Much attention has been focused on the probability of loss of crew (pLOC) as a figure of merit in determining the crew launch aspect of the architecture, and we expressed that the ESAS pLOC numbers were all using the same methodology and that the value was in the comparative results and not in the absolute numbers. Very simply, Ares' clear advantage is in the comparative simplicity of its first stage (the shuttle SRM) and use of a single gas generator cycle upper stage engine. These two attributes alone provide substantial robustness over, for example, a more complex liquid pump fed first stage and a multiengine upper stage - simply put, they are more complex with more moving parts. What Ares affords us, in accordance with the findings of the CAIB, is a crew launch system that has the potential to achieve unmatched safety in human spaceflight history. And this is not just a Constellation 'claim' as some would suggest, but has been validated by independent experts in the field of physics based probabilistic risk assessment. There will be much more provided on this topic as well.
John & mars,I really don't feel comfortable discussing that in public without seeking permission from the panel first.Lets just say that they have been asking questions, we are preparing data for them and some of the team have made contact directly. And the contacts have all been good so far.We have decided to leave it entirely to the panel themselves to control the release of all such materials and discussions for themselves according to their own policies.
Noted that the June 22 issue of AW&ST's coverage of the Augustine Commission (on page 40) didn't have a single mention of Direct but did mention everything else, including Not Shuttle C.
EML-1 and EML-2 are primarily useful for architectures planning to use re-usable landers and ISRU -- neither of which is going to happen cheaply, nor soon.If you aren't, they actually cost more in terms of delta-V than the EOR-LOR/Loiter plan which is currently baselined.Another concern, is that if you fly the Orion separately from the Altair, you have no Apollo-13 style "lifeboat" capability at all and that results in a significant hit to your overall mission safety.Given a fixed starting mass delivered to LEO by two vehicles, the bottom line is that the EOR-LOR/Loiter is THE most efficient means to get to the Lunar Surface and back with the current requirements for Global Access and Any Time Return capability. It delivers the highest payload mass to the surface for every flight -- which is the real yardstick you need to measure things by.EML-2 would make for a truly wonderful staging area for any mission heading out into the rest of the solar system though. If you could assemble all of your Mars (and later Jovian) vehicles there and fuel from the Lunar surface that would make for a stunning capability.But trying to establish that sort of architecture straight out of the gate on day 1 is like planning to build a complete national highways system in a single week. You're biting off more than you can realistically chew in one mouthful, and all you're actually going to end up doing is choking on it -- and a Lunar Landing is already a *really* big bite all on its own without ever trying to complicate it in any way.No, what really you need to do is a very simple business and management technique:1) Identify where you are and what resources you have right now.2) Identify where you wish to be and what resources you need to get there.3) Identify means to break that "giant leap" into a series of smaller, easier, steps.4) Begin the process of achieving each of those steps, in order, in an orderly manner.5) When you achieve the last of those steps you will have reached your ultimate target. Job Done. What's next?Ross.