Aero capture maturity and Lunar cargo

[radarredux]

My initial question is: How mature is aerocapture?<br /><br />The reason I ask is that the t/Space architecture required aerocapture/aerobraking for returns from the Moon instead of plunging directly into Earth's atmosphere for a direct landing. There seems to be a lot of potential value to exploiting Earth's atmosphere that isn't being taken advantage of in the current ESAS.<br /><br />PROPOSAL:<br /><br />Since one of the concerns against the t/Space architecture is that it doesn't provide an abort directly to Earth capability, why not focus on a t/Space architecture for cargo-only trips?<br /><br />Salient features:<br /><ul type="square"><li>The vehicle would be a precision landing vertical takeoff, vertical landing spacecraft that would only operate between the Lunar surface and LEO.<li>It would use aerocapture on returning to LEO to minimize fuel costs.<li>It would be 100% reusable. Only fuel and LOX (and a fresh cargo) would be needed for each trip.<li>It would be autonomous, cargo-only, thus reducing safety requirements.<li>There could be a family of different size vehicles. Initially a small pilot program could test the idea, but it could still be usefull delivering pathfinder-class rovers.<li>It could be used to land rovers on the Moon. Rover projects would need to only concentrate on the rover; surface delivery would be taken care of by the reusable lander.<li>Once humans are on the Lunar surface it could deliver all sorts of necessary cargo to the surface.<li>It could return cargo (e.g., Lunar samples, research results, etc.) to LEO, which would then be returned to Earth's surface by traditional capsule (or whatever).<li>The engines would be kerosene/LOX or methane/LOX.<li>Initially both fuel and LOX would be delivered from Earth's surface, later LOX would be generated on the Moon further reducing costs.<br /></li></li></li></li></li></li></li></li></li></li></ul><br />As experience and confidence is gained, a human version could be put into operations. Then a larger potential number of organizations

 

[nacnud]

I love the idea, it does seem like a logical next step beyond the current CEV, CLV and HLV architecture for cargo delivery.

 

[krrr]

I think aero<i>capture</i>, i.e. braking from a TEI trajectory directly into LEO, is quite difficult, both in terms of navigation and spacecraft structure.<br /><br />Aero<i>braking</i>, meaning several dips into Earth's atmosphere before finally arriving in LEO, shouldn't be that hard.<br /><br />For cargo missions, multi-pass aerobraking is no problem. For manned spacecraft, it is not desirable because of the time consumed and the multiple passes through the radiation belt.

 

[CalliArcale]

Aerobraking has in fact been done several times with great success. It has in fact become the standard method for refining orbits around Mars. Aerocapture hasn't been done yet, and so there's some risk just because it's new and of course has some unknowns. It won't have much margin for error, which is concerning because of the variability of the Earth's upper atmosphere. I'm sure it can be worked out, but it won't be trivial. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[spacester]

Definitely non trivial. <img src="/images/icons/laugh.gif" /><br /><br />The simple key to Aero<b>capture</b> that must be remembered is that the first aerobraking dip in the atmosphere has to dissipate enough energy to get caught in the planet's gravity well ON THE FIRST PASS.<br /><br />That's a lot of deltaV to get rid of for any traditional trajectory to Mars. But, if you're returning from Moon to Earth, you're already in Earth's gravity well.<br /><br />IOW, technically, there's no such thing as Aero<b>capture</b> if you're returning from the moon: you're already captured.<br /><br />For Mars Aerocapture, if you don't kill enough velocity, Mars will be in your rear view mirror cuz you're still orbiting the Sun, not Mars. The same thing goes when returning to Earth from Mars.<br /><br />One of the things ion engines offer is that when you arrive, you're already closely matched with the planet's velocity, so an aerocapture becomes 'easy'. But for good old rocket engine burns - which is the way missions will be done for the most part - you're looking at Hohmann transfers (maximum time of flight) to reduce the arrival deltaV.<br /><br />Therefore, I do not like Aerocapture for manned missions. Actually, I don't like aerobraking either for manned missions, simply because I think you need reliable rocket engines and healthy deltaV margins if you're going anywhere beyond LEO. <div class="Discussion_UserSignature"> </div>

 

[spacester]

RR, yours is an excellent proposal. Earth aerobraking makes a lot of sense for cargo craft returning from Moon. I like the logic a lot. I'm going to find time to ponder it, so far I've just read it once or twice. A few quibbles maybe, but then again I need to look thru it some more before I can even say if the quibbles are valid.<br /><br />Nice job! <div class="Discussion_UserSignature"> </div>

 

[scottb50]

I do have a couple of area I have a problem with. I think we should have a vehicle that operates from LEO to LLO and a separate vehicle, based on the moon, that meets the vehicle in LLO and transfers payloads back to the surface or brings them up. <br /><br />I think the engines should be LOX/LH2 powered with propellant carried as water and broken down using Solar Power.<br /><br />I also think capture into Earth orbit as well as lunar orbit should be done with engines, it worked with Apollo. <div class="Discussion_UserSignature"> </div>

 

[scottb50]

The reality is getting to a certain point in orbit not just entering an orbit. <div class="Discussion_UserSignature"> </div>

 

[radarredux]

> <i><font color="yellow">I think we should have a vehicle that operates from LEO to LLO ... I think the engines should be LOX/LH2 powered with propellant carried as water and broken down using Solar Power.</font>/i><br /><br />If it only moves between orbits, perhaps a solar-electric ion driven spacecraft would be better? It seems that (for cargo) the primary advantage of a high-thrust engine is landing and taking off the surface of the Moon.<br /><br />One potential drawback of a LEO-LLO only spacecraft is that one more docking will be needed. Since automated docking in LEO is already a requirement, I don't know if this introduces any real problems or not.<br /><br />Another potential drawback is that two spacecraft need to be developed, a LEO-LLO and a Lunar-LLO lander. Once again, I don't know if this introduces any real issues or not.<br /><br />The "water as fuel" idea is interesting though. Are there any articles or experiments on the viability of the approach?</i>

 

[krrr]

Even for LEO-LLO SEP tugs, I would consider aerobraking for the return trip back to LEO. After all, no propellant consumption is better than little propellant consumption.<br /><br />The large solar arrays would make good braking surfaces. Of course, care would have to be taken not to overload them.

 

[scottb50]

I can't see any advantage using ion engines. It sort of amazes me how many times someone brings it up and someone else tells them it won't work. The simplest and safest means of getting into orbit is the same method used by Apollo. <br /><br />I also see no drawback having more than one vehicle. Each vehicle can be tailored for a very specific purpose and eliminating multiple uses would free up a lot of cargo or propellant room. As I see it they are basically the same anyway furnishings and specific capabilities being the main differences. <br /><br />Water makes the most sense for use in Space of any available alternative. Humans need it anyway and the more of it you have the easier it is to deal with. <br /><br />When compared to volatile propellants water would be much easier to handle, a single container, instead of two, reduced thermal containment worries, safe handling qualities and zero contamination problems. <br /><br />Using Solar Power to produce Oxygen and Hydrogen gas and a gas storage and transfer system would allow a vehicle or station more than adequate power and cryogenic systems would provide propellant for transportation uses or as Station backup supplies or extended low light periods such as at a Moon or Mars base.<br /><br />I also see a market for using this same approach to have short to medium range cars, that you refuel at your home. A hydrolizer uses standard grid power and a storage system collects and stores Hydrogen. I would think if you could refuel in roughly the same time and with the same level of effort as today a range of about 100 miles would be worth looking at.<br /><br />Where we get water is also not an issue, we have to get it from Earth to begin with just to find other sources, but if found they could be used with this system <div class="Discussion_UserSignature"> </div>

 

[CalliArcale]

I just thought of something that might be of interest to folks in this thread. The Russians experimented with a radical way of bringing payloads back from the Moon. They were going to use their existing Soyuz, which doesn't have enough of a heat shield for the job. So instead of the "easy", straightforward approach used by Apollo (which still has a pretty narrow margin for error), they were planning on an ambitious "double-skip" reentry profile, where heat was dissipated on a shallow skip, and then the vehicle would make a second entry to finish the job. They ran a number of unmanned missions designated "Zonds" to send stripped-down Soyuz around the Moon, after launch aboard Proton. Animals and other biological specimens were sent along in some or possibly all of these. Most were lost to Proton failures; the Proton rocket is today very reliable, but at that point it had been pressed into service far too quickly and really wasn't mature enough for use. There were problems getting them back as well, but they did acheive the double-skip successfully twice. Given that most of the failures had to do with immature technology, it would probably be more do-able today.<br /><br />Many of the Soviet failures in the Moon race had less to do with Soviet inadequacy and more to do with overambitious concepts for which the contemporary technology was not ready. Today could be a different story, though. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[krrr]

<font color="yellow">I can't see any advantage using ion engines. It sort of amazes me how many times someone brings it up and someone else tells them it won't work. The simplest and safest means of getting into orbit is the same method used by Apollo.</font><br /><br />We're not talking about getting into orbit, we're talking about cargo transport between LEO and LLO.<br /><br />It should be evident that electric propulsion is vastly superior to chemical in outer space, as long as time consumption (for instance, several months to the Moon) is not a problem.<br /><br />Electric Isp ist 3000+ sec, chemical Isp is 450 sec at best. This means that for LEO to LLO, in the chemical case more than 65% of the spacecraft's mass would have to be wasted on propellant. For SEP, maybe 15%.<br /><br />I like your idea (using water and then produce oxygen and hydrogen by solar-powered electrolysis) very much.<br /><br />However, how do we efficiently haul the water tanks up to the Moon (or L1) in the first place? Answer: with a SEP tug, of course. Since the tug has large solar arrays, these come in handy as the power source for producing O2 and H2 from the water.<br /><br />Take a look at the lunar architecture proposed by Andrews. It is very elegant and does exactly what I was trying to describe above.<br /><br />That said, of course some serious R&D would be required for a large SEP tug:<br /><ul type="square"><li>Scaling up existing electric thrusters to ~100 kW<li>Deployment of large, lightweight solar arrays (1000 to 2000 square meters)<li>Radiation-resistant solar cells, since the tug spends extended time in Earth's radiation belt.<br /></li></li></li></ul><br />However, quoting Griffin:<br /><font color="orange"><br />Discontinued, descoped or delayed technology projects include nanomaterials, inflatable structures, <</safety_wrapper></font>

 

[radarredux]

> <i><font color="yellow">Discontinued, descoped or delayed technology projects include ... large-scale solar power... and electric propulsion.</font>/i><br /><br />Since the first need for efficient LLO-LEO cargo services would not be needed until at least 2018 at the earliest, postponing the funding on these efforts may not be a major drawback. Solar panel research is finally starting to take off in the commercial sector as demand has finally taken off due to a combination of high energy costs, unreliable energy delivery, and favorable laws. Maybe instead of NASA funding this, in 10 years they could just be a buyer of the technology.<br /><br />SEP will probably continue in bits and pieces -- satellite positioning, small experimental spacecraft by DOE, Pentagon, ESA, etc.<br /><br />Perhaps by 2018 a private company could tap into these more mature technologies (by then) to develop a spacecraft and simply sell commercial services to NASA.</i>

 

[radarredux]

> <i><font color="yellow"> they were planning on an ambitious "double-skip" reentry profile</font>/i><br /><br />I thought they were doing that to land at the higher lattitudes of Russia -- come in close the the equator, and "skip" up north.</i>

 

[radarredux]

By the way, The Space Review has an article this week talking about NASA funding a similar capability through the backdoor with X Prize projects.<br /><blockquote><font class="small">In reply to:</font><hr /><p>According to the NASA press release there will in fact be two prizes “tentatively named the Suborbital Payload Challenge and the Suborbital Lunar Lander Analog Challenge.” Both the space agency and the foundation are expected to work out the details within the next several weeks. It seems that the second part of the competition is oriented towards developing a Lunar Reusable Launch Vehicle (RLV).<br />...<br />If the US can build a vehicle, or class of vehicles, that can reliably and safely launch from the Moon into Lunar orbit and support travel to places such as the Lagrange points or either low Earth orbit (LEO) or geosynchronous orbit (GEO), it will be well on its way to attaining a strong position in the future economy of cislunar space. A new space transportation system using the Crew Exploration Vehicle (CEV) and the Lunar RLV together will provide the US with something that might be thought of as a “manned space maneuver architecture”. The Lunar RLV could provide a growth version of the CEV with enough power and fuel to move easily from Lunar orbit to any point of interest within the Earth-Moon system.<p><hr /></p></p></blockquote><br />Could the X Prize Cup help NASA develop a Lunar RLV?<br />The Space Review<br />http://www.thespacereview.com/article/491/1

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>I thought they were doing that to land at the higher lattitudes of Russia -- come in close the the equator, and "skip" up north.<p><hr /></p></p></blockquote><br /><br />No, there was more to it than that. Now that I think about it, I do recall that some of the ones that failed the double-skip did survive entry. Maybe it was more of a G-loading problem? <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>