Ares and Ares

noosfractal · 2006-09-17 23:38:32

Imagine a solar-powered laser cutting torch in the vacuum of space. (I'm reminded of the qarish paintings on some covers of Wonder Stories and other pulps of the 1930's, in which passenger spaceships are depicted horribly being cut into sections by beam weapons, with the beams brightly coloured of course. How about situating our prospecting ship some distance from a rotating asteroid, and slicing it into manageable hunks as it rotates, just like a baloney sausage?

I don't think solar can do it. Some quick googling yields 0.01 kWh per cubic centimeter as the energy required to "spall" rock (apparently you don't want to melt it because then it'll quickly reset as a tough ceramic). The energy required can vary up or down an order of magnitude depending on the type of rock. So, say you have a Star Wars style CO2 laser with a power conversion efficiency of 30% (state of the art for high power lasers, although diode lasers exist with efficiencies of 65% and there are promises of 80%) hooked up to a 50 MWe nuclear reactor. It'll take you 31 weeks to make a 1 cm thick cut through an asteroid 1 km in diameter (53 hours if the asteroid is 100 meters in diameter).

This sounds reasonable, especially if you are just cutting out "cones of interest," but solar today gets about 0.1 kW/kg, so you'd need 500 tons of panels to get 50 MWe. They are trying to get that down to 1 kW/kg with thin film solar - so maybe you could do 10 MWe for 10 tons by 2025.

Of course, you don't need nuclear or solar, because a rotating asteroid is a huge flywheel (albeit an irregularly shaped one). Generator + contact wheel + rotating asteroid = as many MW as you can eat at 2 kW/kg off-the-shelf (3 kW/kg by 2010).

dicktice · 2006-09-18 14:26:39

Yes--melt it, by all means if the asteroid is rotating and collect the spin-off. How? Details ... details.... As to power: Photoelectricity be damned. How about a space-sail style mirror to concentrate the sunlight to (a) directly melt the surface (b) generate emf for a laser torch (c) accelerate electrons in huge CRT-type guns ... or various combinations of all these. Or, if the solar-sail proves impractical, good old thermal electricity in the form of alternating hot junctions (exposed to the Sun) and cold junctions (shielded from the Sun) and tube-less electronics circuitry, on a grand scale only possible weightlessly in the vacuum of spce, to convert the voltages and direct the currents. Okay--I know: We start with the Moon, and take our time designing special weightless "picks and shovels" for the asteroid prospectors to come. Two lifetimes from now, dammit.

publiusr · 2006-10-27 13:03:44

Back on topic:

There is little practical difference, they both have much the same capabilities. Zubrin's rocket calls for four SSME engines in a side-mounted pod plus the single-segment ASRM boosters. The upper stage on Zubrin's rocket calls for a single SSME class engine too. The NASA Ares-V uses upgraded five-segment versions of the Shuttle boosters and uses five RS-68 engines on the bottom of a wider 10m tank. The upper stage uses a single less powerful J-2X engine.
Neither rocket is really powerful enough without nuclear engines to go directly to Mars.

And now we have this option:

http://www.directlauncher.com/

The point is to get some engines under an ET as quickly as possible.

Direct (in metal) as a reality is better than a superior Ares V that only exists on paper.

RedStreak · 2006-10-27 15:51:26

Not a bad alternative plan. Question is are the people proposing this are actual space engineers or mere "enthusiasts".

Devoting a seperate launcher for the booster stage would give it more capacity, but would it put a cramp on cargo that can be carried?

GCNRevenger · 2006-10-27 20:40:12

More importantly though, it deprives NASA of a Saturn-V class heavy lifter which would, I think, really be nessesarry for a Mars program barring the reintroduction of nuclear rockets. Even with, the biggest varient of the Direct rocket cuts the payload kind of close. The expense, both in dollars and political capital, that would entail may well exceed any savings from the Direct plan. I don't buy the supposed savings figures either, the external tank still requires stretching, the launch pad still requires rearranging, the J-2X still needs developing and each Lunar sortie still requires two launches.

neviden · 2006-11-03 07:22:45

i like it more than 1.5 variant..

More importantly though, it deprives NASA of a Saturn-V class heavy lifter which would, I think, really be nessesarry for a Mars program barring the reintroduction of nuclear rockets.

since we need about 500 MT to go to mars we have to send it to LEO in small pieces and assemble them it doesn't make that much of a difference if they are 130 MT or 100 MT pieces.. you sent them to LEO, put them together and when ready send orion with crew..

Even with, the biggest varient of the Direct rocket cuts the payload kind of close.

bigest variant (with upper stage) is 100 MT to 60x100 orbit.. that's 200 MT maximum combined weight.. that's more than 22 + 130 MT maximum for Ares I + V.. and since most of it is propelant, i don't think why it couldn't be done..

The expense, both in dollars and political capital, that would entail may well exceed any savings from the Direct plan. I don't buy the supposed savings figures either, the external tank still requires stretching, the launch pad still requires rearranging, the J-2X still needs developing and each Lunar sortie still requires two launches.

no need for 5 segment boster, no need to develop 2 new launch vehicles.. lower cost to run it.. and since this new rocket would be "manrated" with escape tower when it blows up it would still be safer than shuttle.. not prfect, but we are talking about rockets.. soyuz is not perfect, but it hasn't killed anyone in decades..

and later, you could make reusable lander (that would use LOX at least) that would meet in LLO with orion + EDS launched on one 100 MT (or ever 70 MT if that would be feasible.. 22 MT orion + 58 MT EDS?) single rocket.. (Ares V would not be manrated, so you would always have to send crew with different rocket)..

for ISS you would have fuly fueled orion sitting on top of 58 MT cilinder full of stuff, if the rocket blows up and escape tower saves crew then who cares.. if it does not, you dock with orion to cilinder in LEO, fire engines to get to ISS, pick up cilinder with robotic arm (like HTV plans to do), detach orion from cilinder and dock it with ISS.. crew replacement and twice the cargo capacity of the shuttle.. you could even scap shuttle and NASA could still deliver everything it promissed it would..

it would be cheaper and you could develop 5 segment boosters, add one more engine (or 3 more for full ares V), extend fuel tank and get 130 MT to LEO.. less money spent on moon, new rockets, upgrades,... means more money for mars and elsewhere..

what's not to like?

GCNRevenger · 2006-11-04 08:08:05

no need for 5 segment booster, no need to develop 2 new launch vehicles.. lower cost to run it...
...it would be cheaper and you could develop 5 segment boosters, add one more engine (or 3 more for full ares V), extend fuel tank and get 130 MT to LEO.. less money spent on moon, new rockets, upgrades

No. The 1.5 mission plan only requires 1.5 vehicles to be developed... the Ares-V will share engines, avionics, upper stages, factories, and launch facilities with Ares-I. By building Ares-I, the cost of developing the larger Ares-V is greatly discounted. There is virtually no difference between the boosters and little between upper stages other than the size of the fuel tanks.

And you didn't read the fine print, that all the variants of Direct all require the creation of an additional new engine, the "RS-68 Regen:" presently the RS-68 isn't regenerative and operates at low pressure, which while cutting its efficiency somewhat makes the thing ten times simpler than SSME give or take. RS-68 is also in no way man rated, and the added engineering and testing required (especially to determine what telemetry indicates imminent failure) would be both expensive and time consuming.

Modifying RS-68 to be regenerative and run at higher pressure and be man-rated would surely take about as much development money and time as making the five-segment boosters in the first place. Plus, the additional production cost of the more complex engine would definitely wipe out the savings of needing 1-4 fewer of them (Moon-Mars), maybe even driving up the cost versus 1.5.

And consider, that if we are going to build a 130MT variant of Direct with five-segment boosters some time later anyway, then why not build it right now? Then you could take one of those boosters, slap a mini-EDS on top as a second stage, and put the capsule on top of that for a cheap and safe crew launcher. The combined mass would be enough for Moon missions, and there wouldn't be a need to build a "lite" version of Direct... Oh wait, NASA is already doing that, except trading the expensive man-rated "RS-68 Regen" for a bigger main tank (as RS-68 was designed for to begin with), developing Ares-I first instead of Ares-V, and not developing a smaller varient.

Also, I reject this notion that it will "be cheaper to operate one rocket" as unfounded speculation, particularly since the "1.5" rockets are so similar and will be built, assembled, and launched in the same factories and launch facilities most likely by the same people.

since we need about 500 MT to go to mars we have to send it to LEO in small pieces and assemble them it doesn't make that much of a difference if they are 130 MT or 100 MT pieces

Absolutely it does! That ~500MT figure cited includes at least some use of native Martian fuel made by ISRU, so for safety the ISRU plant/ERV needs to be sent to Mars separately prior to the crew, as in Zubrin's MarsDirect and NASA's DRM plans. This divides up the mass of the mission, and in the case of MarsDirect a 130MT class rocket is the minimum practical size to deliver the payload in only one launch (and I think that is borderline). And for NASA's DRM, the ERV and ISRU/ascent vehicles each weigh ~90MT so they would fit, but to push them to Mars with a TMI booster under 100MT you would have to use nuclear rockets. On the other hand, if we had the big 130MT Ares-V, just stretching the EDS stage should be sufficient. Plus, as an added benefit, the chemical booster could loiter in Earth orbit longer than a nuclear one in the event of a delay.

Point being, the combined mass of the launch vehicles isn't very relevant, the capacity of single launch is. In MarsDirect, either the rocket has the power to throw 40MT to Mars or it doesn't, in DRM either the rocket has the power to lift the TMI stage or it doesn't as cutting the TMI stage in two isn't a good idea to bank on.

As far as the Moon, a ~70MT rocket is probably overkill if you just want to put the Orion capsule in Lunar orbit. You could launch a modified Centaur TLI stage on a second Ares-I, mate the two, and go to the Moon that way for probably the same money. Plus, this gives an "entry point" for COTS if they can deliver the Centaur instead.

not perfect, but we are talking about rockets.. soyuz is not perfect, but it hasn't killed anyone in decades

Nonsense, the are a variety of problems that Direct would have that Soyuz does not, such as the simple fact that the huge main tank of liquid hydrogen exploding makes a much, much bigger bang reguardless how an explosion starts. The biggie I think though is one you can't fix, which is the fact that you would put people on top of a rocket that has eight booster segment seals right against the main tank. This is a big problem, and even when the boosters are used "properly" unlike Challenger, the same thing nearly killed Atlantis once. We got lucky that time and the leak faced away from the tank, and I think Griffin is taking a substantial risk on ~15 more Shuttle flights. This is not a huge risk, but I think its too big a risk for manned rockets, and is something that Ares-I doesn't have to worry about but Direct does. How much more reliable does Direct have to be, with triple the engines even, to make this failure mode average out versus Ares-I? (Thats a rhetorical question BTW, it really can't)

You also place far too much faith in the launch tower, which when used you still have a good chance of being maimed and killed. You are talking about an ~10G+ acceleration while retaining attitude control, but more importantly is the question of what determines its activation? Are the sensors and the warning signs they detect reliable? Do these warning signs occur soon enough before "kaboom" to escape? What about sensor data that doesn't fit the predetermined "punch out" parameters when the thing fails? Here is where Ares-I has a big advantage, that because the big SRB is so simple that when things "go bad" its obvious, and thanks to their construction bad things don't happen very fast. Compare this to a bank of running turbo pump engines?

And, even if it does work, the lower acceleration of Direct means you are going to come down in the middle of the ocean instead of closer to European/African shores. Finally, you must be out of your mind to talk about "good enough" safety in a launch vehicle, that the embarrassment and loss of credibility of NASA's new rocket killing its crew could be fatal to manned spaceflight. "You can't even put people into orbit safely!"...roared the congressman.

or ISS you would have fuly fueled orion sitting on top of 58 MT cilinder full of stuff

Pish the ISS... it can't do anything worthwhile even with that kind of payload, and the stations' cargo needs will be supplied by COTS before too awful long anyway probably. Plus, Direct isn't suited for construction, that many of the ISS components aren't sturdy cylinders, but rather loose bits clamped down to the inside of the Shuttle bay. Plus you have to remember, that the ISS construction was designed with Shuttle's arm in mind, and you can't just place a cargo pallet free-floating that close to the station so its arm can pick pieces off of it. Then there is the simple fact that you are throwing away this big rocket when a small one would do just fine for less money and less risk.

I don't like the Direct plan... it has too many compromises in the name of expediency, isn't as safe, and overall displays a terrible fear of undertaking big projects under the guise of cool pragmatism. Also, do not be deceived by pretty talk of upgrades: one of the main reasons that Shuttle is so expensive is because of the incessant upgrading. No, its better to build it right the first time (BIG) instead of future modifications. It really doesn't save money, saddles us with a useless whimpy "kinda sorrta heavy" intermediate rocket (which probably costs as much as the 130MT heavy), and substantially increases risk to the crews.

SpaceNut · 2020-06-28 18:26:49

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#151 2006-09-17 23:38:32

Re: Ares and Ares

#152 2006-09-18 14:26:39

Re: Ares and Ares

#153 2006-10-27 13:03:44

Re: Ares and Ares

#154 2006-10-27 15:51:26

Re: Ares and Ares

#155 2006-10-27 20:40:12

Re: Ares and Ares

#156 2006-11-03 07:22:45

Re: Ares and Ares

#157 2006-11-04 08:08:05

Re: Ares and Ares

#158 2020-06-28 18:26:49

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