Total Members Voted: 102
Voting closed: 02/12/2016 08:01 pm
Quote from: ncb1397 on 12/20/2016 09:30 pmI always questioned this assumption. Sure, supersonic atmospheric entry and supersonic atmospheric retro-propulsion introduces all kinds of problems in the design of a lander, but why not do the following:1.)zero out the horizontal/vertical velocity at 25 km altitude.You'd have to use a lot of fuel to do that, so that's your tradeoff. Especially if you mandate that every kg of mass you want on the surface of Mars has to use this method. So using the Mars atmosphere reduces the amount of fuel that you need to bring along with you (or ship ahead).QuoteIn my opinion, propulsive EDL and ascent on Mars is completely doable(total delta-v is less than earth to LEO) and supersonic entry and supersonic retro-propulsion will lead to all kinds of compromises in terms of design that will mean a whole new system will be required for doing anything else efficiently(whether that is in-space maneuvers or landing on anything that isn't Mars).Of course if you perfect being able to land on Mars and Earth using retropropulsion, then those same vehicles can obviously land on an airless world too - which is what Musk has stated. So whoever wants to use one for going to the Moon would be able use one (and Musk might even sell to them).But otherwise it's a question of money as to what method is used, and Musk has decided what he wants to use...
I always questioned this assumption. Sure, supersonic atmospheric entry and supersonic atmospheric retro-propulsion introduces all kinds of problems in the design of a lander, but why not do the following:1.)zero out the horizontal/vertical velocity at 25 km altitude.
In my opinion, propulsive EDL and ascent on Mars is completely doable(total delta-v is less than earth to LEO) and supersonic entry and supersonic retro-propulsion will lead to all kinds of compromises in terms of design that will mean a whole new system will be required for doing anything else efficiently(whether that is in-space maneuvers or landing on anything that isn't Mars).
Landing a vehicle designed for aerodynamic entry on the moon wastes fuel/payload.
Stripping the heatshield and aeroshell out of it adds payload pound for pound.
What tips the balance is that most surfaces in the solar system are either not survivable or not covered in an atmosphere.
This discussion is only about NASA returning to our Moon. What SpaceX may or may not do beyond our Moon is OT.
Designing, building, testing and operating only one vehicle is far less costly than having to do that with two designs. Being less efficient with fuel is an acceptable tradeoff, especially when you operate your own fuel depot system.
The proposed SpaceX ITS is planned to be able to land almost 1,000,000 lb of cargo on the surface of Mars, I'd say that should meet the needs of any lunar activity for quite a while, even if it still has to carry a heatshield.
Just to flesh out ideas on how Moon and Mars don't have to be in conflict with each other.
Quote from: ncb1397 on 12/24/2016 05:46 pmJust to flesh out ideas on how Moon and Mars don't have to be in conflict with each other.Your slide deck is like every other hardware-oriented slide deck - it ignores the most important question. Why should the U.S. Taxpayers fund NASA to go back to the Moon?The reason we haven't returned to the Moon is not because of a lack of hardware concepts or ideas, nor the technical ability.What we have lacked is the national need. Identify that, get everyone to buy into it, and the hardware part will take care of itself...
So, not only does "everyone" have to agree on what it is we are going to do, the motivation has to be the same as well? In some perfect utopian/orwellian idealistic society, that may be possible, but it is an impossible standard to achieve.
Does everyone agree on the F-35 program?
Really it could actually only come down to a handful of people.
Take the Europa mission. Hardly anybody in the government wanted it but some scientists in the decadal survey placed it on a priority list. It really came down to one person, Rep. John Culberson, whether it happened or not.
Anyways, a Moon program doesn't require a constitutional amendment that needs anything like 3/4s of the states. Really all you need is simple majorities in a few committees and a president that isn't completely hostile to the idea.
The fact is, you can get hawks and doves to support human space flight in general and human space exploration specifically. Doves can support it as a model of cooperation of an international coalition of peaceful coexisting governments. Hawks can support it to maintain the high ground over the Chinese/Russians. They don't need the same reason.
edit: Most of the debate is on destinations and missions, not whether we will do human space flight or not. That is why you should build a completely destination agnostic approach. That way, a change in destination doesn't require some massive decade long engineering effort to accomplish. The flexible path is a good one.
The systems that NASA is working on today have multiple flight profiles and possible utilization schemes.
I disagree. The SLS is too expensive to use, and the Orion is limited to the region of our Moon and too expensive to use too. Plus both are NASA-only assets, which means the private sector won't use them, nor would possible international partners. Which is why they are actually a liability for NASA, not assets. IMHO.
I disagree that SLS and Orion are NASA-only assets.
The private sector use of the ISS is an example of that, even though NASA operates the vehicle, commercial use is not precluded.
Also, I seem to remember a member of the Saudi Royal family riding on STS, and so not even space tourism would be out of the question.
As far as operational cost of these programs, it seems you have information that others don't. What is the operational cost of SLS and Orion?
Quote from: ncb1397 on 12/24/2016 08:05 pmSo, not only does "everyone" have to agree on what it is we are going to do, the motivation has to be the same as well? In some perfect utopian/orwellian idealistic society, that may be possible, but it is an impossible standard to achieve.Everyone in the funding loop. Even the public was not enamored with the Apollo program until just before it succeeded, but the political need was known to the politicians, and they gave it a tremendous amount of funding because of the perceived need.QuoteDoes everyone agree on the F-35 program?The F-35 was originally funded because it was going to solve a national need. It was always going to be a massive program, and I would wager no one is surprised that it has had problems. But it is still going to be solving a national need, which in this case is defense of our nation.What is the need that sending government employees to the Moon solves (or Mars for that matter too)? Apparently nothing bad happened during the past 45 years since we left the Moon, so waiting another 45 shouldn't be a problem, right?
QuoteThe private sector use of the ISS is an example of that, even though NASA operates the vehicle, commercial use is not precluded.Commercial use is one of the planned goals of the ISS. And the key word here is "planned", whereas the SLS has no real forecasted need that it satisfies, and it was definitely not built with the private sector as a potential customer.
QuoteAs far as operational cost of these programs, it seems you have information that others don't. What is the operational cost of SLS and Orion?No one in the public knows for sure, and NASA is even keeping Congress in the dark. But we have lots of recent analogies that can be applied, such as Shuttle program costs that are comparable, and the fact that both the SLS and Orion are 100% expendable vehicles. As someone that has a background in product cost rollups, this is not hard stuff to estimate. YMMV
Just to flesh out ideas on how Moon and Mars don't have to be in conflict with each other. And you can do both using assets and technology that NASA already has or is over half-way through the development pipeline.
F-35 was fifth generation fighter jet.Roughly, F-35 is same reason you get new car models each year.
One could argue that we can redo the Shuttle and continue ISS for decades more.One could also argue that "we" tried to do the LEO thing and it didn't have much upside to it.
So exploring the Moon doesn't "have to" have crew, but it makes sense to use crew in order to explore the Moon.
There are many things which could be done with the Moon in the future, but a near terms question is does the Moon have minable water. If it does, then one can do many things on the Moon.
As stated just above, NASA is not hiding the cost, they don't know it yet. The unit cost of a launch is closely related to the frequency of launch, which is to a great extent controlled by Congress.
Quote from: ncb1397 on 12/24/2016 05:46 pmJust to flesh out ideas on how Moon and Mars don't have to be in conflict with each other. And you can do both using assets and technology that NASA already has or is over half-way through the development pipeline.1.5MW is not sufficient for crew transfer given that kind of mass. Or what are the SEP specs?
Quote from: Oli on 12/25/2016 09:56 pmQuote from: ncb1397 on 12/24/2016 05:46 pmJust to flesh out ideas on how Moon and Mars don't have to be in conflict with each other. And you can do both using assets and technology that NASA already has or is over half-way through the development pipeline.1.5MW is not sufficient for crew transfer given that kind of mass. Or what are the SEP specs?These were the specs that I was working off of:fuel - 35,000 kg Xenonsolar power - 1500 MW @ 1 AUengine power - 1375 MWengine thrust - 23 Nisp - ~9500 secondsMars- ~50% powerEarth- 100% powerWhich would yield approximate maneuver times of the manned interplanetary leg of:-LEO to EML-1 - 7000 m/s (SEP ~30 months)...unmanned-EML-1 to TMI - 650 m/s (chemical, PL stage 1), 200 m/s (SEP ~1 month)-TMI to HMO - 600 m/s (chemical, PL stage 1), 600 m/s (SEP ~3 months)-HMO to TEI -140 m/s (chemical, ITV main engine, PL stage 2), 1350 m/s(SEP ~5 months )-TEI to earth/moon capture - 1300 m/s (SEP ~3 months)It is a bit sluggish at Mars(5 months for TEI). If you look at slide 7 that I updated on the slide deck, that is a potential upgrade path but it uses TRL 6 150 W/kg solar panels vs TRL 9 80 W/kg. That would give you 80% SEP thrust at Mars. Otherwise, to save chemical fuel for TEI, you might look at aerobraking in other maneuvers with the solar array or a second tug that does the TMI burn(which adds a SHLV launch).