Earth to LEO - discuss

srmeaney · 2005-06-08 04:19:17

The vehicle could conceivably experience substantial drag during its entire flight. This drag would work constantly to slow the vehicle, just as it does for a typical airplane. When we start using that drag force to steer or change speed, that's technically aerobraking. Nobody thinks it's unusual when an airplane pilot throttles back or raises his flaps. He's just flying the plane. Likewise, it's no more unusual for an ATO vehicle to use aerobraking as well.

CM Edwards, would a ceramic anchor on a tether be an option? The craft is going to deorbit rather quickly whether its aerobraking with big inflated bags or droping an atmospheric drag anchor. Will it have to just sit out there and aim for minimal thermal deflection on the very edge of space as friction slows it down over a year while it takes on fuel and drops in from a clark orbit using fuel to slow descent?

Fledi · 2005-06-08 05:43:49

Nice idea with the anchor, but as far as I understand this, the large surface area of the dirigible would force it down much more rapidly even from low earth orbit than a conventional satellite.
The anchor idea itself is something that might be worth a look at for deorbiting normal spacecraft, though.

dicktice · 2005-06-08 06:24:32

Not clear how the dirigible gets from 17,000 mph down to match the speed of the rotating atmosphere.

Fledi · 2005-06-08 07:04:11

Through being a huge lifting body design that uses aerodynamic lift to descend into higher pressure layers of the atmosphere only when its speed has become low enough not to exceed the hulls heat limit.
The final 30-20km altitude to the ground will be difficult with that flimsy hull, of course, but it doesn't seem to be difficult to slow down to the speed of the atmosphere before that.
But I'm sure C M Edwards can tell us more about that.

C M Edwards · 2005-06-08 12:59:44

Not clear how the dirigible gets from 17,000 mph down to match the speed of the rotating atmosphere.

All right, I'll try another tack...

Everything posted previously about ATO re-entry boils down to the following:

Get in close enough to the surface to catch some wind, then shut down the engines. That will slow down an ATO vehicle enough to bring it back into the thicker atmosphere. Wind resistance alone will eventually bring it to a halt.

The vehicle has so much sail area that that's really all it takes. (Some thrust may be needed to keep the trajectory shallow enough, but only a little, if any.)

The ship doesn't need to be all that low for this to work in just a few days. Take it down to about 100km, shut off the engines, and mother nature will take care of all the rest.

dicktice · 2005-06-08 14:29:00

Straight down thrust, with aerodynamic angle of attack authority, assuming an elongatd envelope. Alternatively, perhaps a so-called flying saucer configuration, with omnidirectionally vectored thrust from the centre....

srmeaney · 2005-06-09 04:34:47

Quote
Not clear how the dirigible gets from 17,000 mph down to match the speed of the rotating atmosphere.

All right, I'll try another tack...
Everything posted previously about ATO re-entry boils down to the following:
Get in close enough to the surface to catch some wind, then shut down the engines. That will slow down an ATO vehicle enough to bring it back into the thicker atmosphere. Wind resistance alone will eventually bring it to a halt.
The vehicle has so much sail area that that's really all it takes. (Some thrust may be needed to keep the trajectory shallow enough, but only a little, if any.)
The ship doesn't need to be all that low for this to work in just a few days. Take it down to about 100km, shut off the engines, and mother nature will take care of all the rest.

Its going to have to reduce its profile to the Heat shield it intends to hide behind on the way in, or use up its gasses in deceleration.

Fledi · 2005-06-09 11:25:52

Normal reentry as we know it only takes a few minutes, high g loads and a heat load of an order of megawatts/square meter. When the reentry takes days and with the heat load spread out along the much larger ballon hull, it should be possible to come down to, let me guess, a few watts/square meter, no problem to deal with it only by radiative cooling without exceeding the hulls heat limit, even if it's just a few hundred °C. The g load can be divided by 1000, too (so 0.005g instead of 5g) , if you go with 5 days insdead of 5 minutes, but with such a large hull it might even be the more serious issue than the heating up.

PS.: I'd be as surprised as you are maybe if I wouldn't know about the calculations the ARCHIMEDES mars balloon guys did which lead them to develop that one WITHOUT any heat shield for reentry.

C M Edwards · 2005-06-09 13:13:43

PS.: I'd be as surprised as you are maybe if I wouldn't know about the calculations the ARCHIMEDES mars balloon guys did which lead them to develop that one WITHOUT any heat shield for reentry.

Wow! I didn't know that the ARCHIMEDES probe was designed to enter Mars atmosphere without a heat shield. It's gratifying to know that my own compressible flow calculations didn't include my usual order of magnitude error... :;):

The mission description says they're including a "thermal protection blanket" of unspecified dimensions for the balloon, though. Looks like they're expecting more heat than their balloon fabric can handle by itself.

Fledi · 2005-06-09 16:40:56

Yes, they were doing some tests with the hull a year ago, a pity I was only beginning to study when they started the project, so I don't know that much about it.
But that idea with going without a heat shield came along the way, they had difficulty to get the whole thing down to the mass the piggyback launch with an Amsat probe would allow them, so they will inflate it in space.

Mars_B4_Moon · 2006-03-25 05:40:46

some good info here

http://www.bautforum.com/showthread.php?t=35965
http://www.spacefellowship.com/Forum/about1373-0.html

cjchandler · 2006-06-30 13:43:04

Sorry that this is at the end, I just joined, but here's my two cents. Any craft that must use megawatts of stored energy per second is inherently dangerous and ineffecent. Since failure must be kept to a minimum this adds cost and voila- 10,000 dollar per Kg. While conventional ideas like adding an air breathing first stage, reusablitiy, and small workforces can help, they are not going to provide the cost savings looked for. Rockets don't seem too complex at first glance but the exhaust velocities that are limited nessesitate all the smallest effeny increases possible, light weght tanks and so on to keep the rocket a reasonable size. This is what makes small rockets expensive. As for big dumb boosters, they may be a bit of an improvment, but the specail facilities needed to make them and launch them, along with the cost of raw materials and labour drive the cost up. Therefore what is needed is way of providing those raw megawatts safelly and cheap enough so that it can get by with a 20% effentcy. Chemical rockets are not going to provide that kind of power, though not expensive in themselves, the tanks and engines are. The only possiblity I see that is reasonable is beamed power, or accelorating slowly so you don't need megawatts a second. My views on slow acceloration are posted on "airship to orbit" thread, but here I'll discuss beamed power. Microwaves spread out too much and are expensive and inneficent to genorate. Lasers are way too expensive, however there is no reason one has to use a laser to beam light. Given a resonably large reciver, ordinary light from the sun should be able to be focused on spacecraft. I advocate building stationary large variable focus mirrors and using cheap (read free) solar power. How might this be done economically? Baloons, 30 km up with clear tops and reflective bottoms filled with hydrogen could collect large amouts of light given a large enough diamiter and a hard ring. If the baloon material was streachy the foucus could be ajusted by changing the internal pressure. It could be aimed with small electric propellers. Maybe this is radicall enough to be cheap. At least there is low start up costs. The spacecraft it's self could use the light to heat hydrogen to nuculer rocket temperatures.

GCNRevenger · 2006-06-30 17:04:35

Well, if vehicles with megawatt-class power outputs are so bad, you might want to clue in the commercial aviation industry... But if you mean the combination of power density and inertia, then that is a more valid point.

I disagree with both your points,

Our ability to control and manage ultrahigh power outputs has increased steadily since the industrial revolution, and will continue in the future. It is not that far today from the threshold of truely efficient combustion-powerd spaceflight. We could, this very day, build a medium two-stage spaceplane with reliability not (though not the efficiency) infinitely less then what would be needed to expand humanity into space.

The low energy density of chemical fuels is a problem, but materials science is not by any means sitting still, and I think that it is entirely possible that we will be able to make a really efficient SSTO space vehicle when the time comes for us to leave the cradle.

That failing, the biggie you left out is the space elevator, which we are not quite there yet, the material strength required to make the cable is within sight and could be possible. I believe one of these two options are the only practical concepts for a common man to be able to leave the Earth.

I strongly doubt that beamed power is a practical answer, I agree the problems with microwave power are too signifigant to overcome and lasers share many of the issues... and also the balloon-solar-mirror idea.

First of all, a balloon on the kilometer scale needed to collect gigawatt amounts of power at that altitude would be very difficult to build or deploy. You are talking a balloon of crazy size, with a cross-section of around 5-10 million square meters (for a modest sized hydrogen rocket) which would have to float up through the jet stream and all that

There are also practical concerns, cheif among them is how do you direct such a concentrated beam of energy? It would be so bright, that it would simply melt mirrors of practical size/mass. The notion that the balloon's shape could be changed on the time scale of a space vehicle launch is silly too, you could never manage it with something this size.

Then there is the hypothetical vehicle, which will have to be above or at least as comperable altitude to this city-balloon, and if the balloon is high enough to be stable for very long periods then the vehicle will have to get up pretty high too. Also is the problem of collecting this energy, the "Cube/Square Law" states that as the vehicle's volume increases the surface area increases much less.

Since the maximum power the vehicle can absorb is controlled by the maximum temperature of the collector, the size of the collector ultimately determines the maximum power collection capacity. Because this increases only a little when the volume increases alot, this means that as the space vehicles get bigger it will make them harder and harder to launch.

Edit: as a side note, the cost of the actual energy to do the launching is presently trivial, and even in the future it will probably not be a majority of the cost, so the "free" aspect of solar energy is irrelivent.

Edit-edit: For a 9,000MW solar balloon, you are looking at around three kilometers in diameter.

Edit-edit-edit: Thats assuming 100% collection/transmission efficiency. Say a reasonable figure of 66%, and then you are talking four kilometers. The largest balloon ever launched, a 60 million cubic feet science balloon by NASA, was only around 150m in diameter inflated.

cjchandler · 2006-06-30 19:16:49

I know it was a bit crazy, I'm just fed up with the lack of progress with conventional rockets. Think about the miracles we can do with carbon fiber re-enforced composits and the like, way better than 60's materials for the Satrun V. Yet it was more reliable than the current designs, although I don't know how much composites they use. The space elevator would be very handy, but I distrust the nanothechnology people. How many times have they been claming to have cheap dimond everything? Lots, but we're still a long ways off. I don't think the ballon idea, though absolutly insane, is as bad as you think it is however. I've been thinking, the balloon would's nessiarily have to change focus, if it was set to foucus at, say 1400 km. Then the spacecraft, lifted up above most of the atmosphere with another baloon could accelorate over a long arc. The aiming would still be a problem, but I think a group of propellers could do it (maybe) there's virtually no turbulence at 30 km altitude. As for the massive size, yup, that's a stumper. however, lets just say for the sake of argument we just want to send a tiny capsule up with two or three people. The weight might be around 3000 kg (like the t/space craft) and at a exhast tempurature of 6000 K (got from -http://www.medianet.pl/~andrew/SPBI115.HTM) an exhast velosity of 13200 m/s. so thats 3202 kg of hydrogen if we add another 1000 kg for tank and engine. That means total energy needed is about 279043132162.6148 joules. Over five minutes taht would require 715495.211 square meters of mirror. Over 20 baloons that's a diamiter of about 200 meters, not too much larger than the nasa balloon. I agree however that this is unlikely to work.

GCNRevenger · 2006-06-30 22:02:33

Rocket engine performance has pretty much hit a wall because of the energy density of their fuels, that much is pretty clear. Because rockets have to carry so much fuel, and fuel is cheap, rocket builders must weigh the cost of building the fuel tank versus simply carrying more fuel. This calculation was most recently done for the EELVs, and sticking with Aluminum made the most sense, because its cheaper to make bigger tanks out of it than smaller ones out of composites. The same is slightly less but probably still true for larger expendable rockets. Likewise, since all rockets (all of them, Shuttle is a dead program) are expendable, today's engines are geared tward being powerful and cheap. Which all makes perfect sense given what we were doing with them, the occasional launch of light-to-medium payloads to fairly high energy orbits, and why nothing has changed.

Now, we are going to the Moon and Mars, so we need somewhat bigger rockets, but still don't need large masses or crews. The biggest reason you don't see new technology really being used is because:

-NASA & the US Gov't has a history of technologic over-reach
-There isn't any great need for advanced launch systems

NASA and the government have looked into very advanced SSTO vehicles to support either a vast array of space-based ballistic missile interceptors (which would need very large numbers of light/medium launches), be a suborbital spy plane/nuke bomber, or to replace Shuttle in its continued mission to bodly go in circles forever. All the concepts, (NASP, DC-X, X-33) were and probably still are beyond our reach, choosing to go with the hardest possible route despite all reason.

The biggest obsticle though is the lack of a need, if we really were bent on medium-scale Lunar mining or setting up a small Martian town, then we would definately see development on a real reuseable launch vehicle. We really could do it today too, cryogenic engine development hasn't completly stopped since SSME, and we could make an engine with comperable performance but much higher reliability. Conventional turbine jet engines not unlike those on fighter planes or the SR-71 Blackbird have built to operate at up to Mach-5. Heat shield materials that are either made entirely of metal or are far stronger then the brittle Shuttle RCC tiles (like for DARPA's X-40 SMV) are available too. A two-stage vehicle with Delta/Atlas class payload or a dozen-plus seats is possible without anything brand new. Slushed Hydrogen could be used perhaps if the upper stage got too bulky.

As far as the balloon idea goes, all that trouble for a little three-tonne capsule? And it takes how long to acend? No, I don't think that will ever work.

cjchandler · 2006-07-01 12:38:40

I understand that at the moment there are few comercial applications in space besides comunication satalites, but I think demand would be greater if the prices weren't so high. Of course this gets back to which comes first, the chicken or the egg. So I think either one, a sudden desire to get into space or a suddenly easy way to get into space would do the trick. Many people have a desire to visit space and weightlessness already, look at the popularity of even the suborbital flights. How many people have signed up for virgin galactic? It's quite large though I don't have the exact figures. Therefore, I think we should concentrate on bringing up tourists. Once we can do that relitivly cheaply, there will be a massive demand for cargo and supplyships. However, even besides money, there is saftey for tourists. A comercially viable tourist launcher could have tickets prices in the millions, but it must be very safe. Even if a highspeed carrier aircraft with a rocket could lower prices, I'm not sure it could be made safe enough. In the public's eyes sitting on top of practicaly explosive fuel isn't a good deal no matter the cost. I might venture to state that the reason the suborbital flights sell well, even in advance, is because their engine is safer, and apears safer to the public. Laughing gas and tire rubber? Can't be too dangerous. I think you have a very good point about demand. I think that the easiest, but not only, way to make it cheaper, is to sell ticket comercially on a very reliable launcher.

GCNRevenger · 2006-07-01 14:06:12

The demand really wouldn't be very high, already space communications satellite business is much slower then it was twenty years ago with the advent of superhigh capacity fiber optic cable, which means that launch would have to be far cheaper to be competitive. There are applications that can only be served by satellites, weather or remote internet access, but these are few and far between.

VirginGalactic and other space tourism outfits will never be able to send up any large number of people, the ones that want to go up just don't have the money. Orbital tourism is a pipe-dream for the forseeable future, orbital vehicles require hundreds of times the energy and a dozen times higher reentry temperature & pressure. As far as chickens and eggs, cheap orbital launch will have to come before orbital tourism.

I think we can make a vehicle reliable enough today. Efficient probably not, but reliable enough. SSME-class engines with a one-in-thousands chance of failure have been tinkered with and half-built, jet engines are more than mature enough, and aerodynamics are pretty well understood. The public doesn't seem to have a problem sitting inbetween very thin pressurized tanks of kerosene, basically a fuel-air bomb (see "Daisy Cutter" or MOAB), with spining turbines that could punch holes throughout the vehicle if they came apart in commercial airliners. The public would simply be wrong.

That said, the simple "primativeness" of suborbital tourism vehicles on the other hand exposes riders to fairly signifigant risk, since nobody in the business - not even Burt - has the money to really do it well. Note that the test pilots for "SpaceShipOne" didn't even have pressure suits.

cIclops · 2006-07-02 02:24:54

VirginGalactic and other space tourism outfits will never be able to send up any large number of people, the ones that want to go up just don't have the money. Orbital tourism is a pipe-dream for the forseeable future, orbital vehicles require hundreds of times the energy and a dozen times higher reentry temperature & pressure. As far as chickens and eggs, cheap orbital launch will have to come before orbital tourism.

The ratio of the energy to attain orbit to that to reach the same height is: (m*g*h+0.5mv^2)/ m*g*h or approximately a factor of 32. To take SS1 from 100kms to ISS orbit at 400kms would require about 36 times more energy.

And after suborbital tourism will come suborbital transportation, fast worldwide point to point services. Yes it will be a long time (2020+) before orbital tourism literally takes off other than for the super rich.

cjchandler · 2006-07-02 04:49:22

GCNRevenger - you're probably right about cheap launch before orbital tourism, but I've heard that there is even a waiting list to ride the Soyuz, though there is quite a steep markup. ( if sub orbital costs 200 000 dollars, than multiplied by 36 is only 7.2 million. I know that's a crude calculation, but the Russians are defiantly making some money) I'm willing to wager that a good deal of their success comes from the Soyuz’s proven reliability, it's quite a bit safer than the space shuttle. If Biglow does build his hotel/cruise ship thing and is able to by Soyuz’s to transport passengers, I think you would see a lot more space tourists, right now the Russians obviously have other obligations. Never the less that's unlikely, any I think anything like this will be a long time coming, barring some breakthrough...

GCNRevenger · 2006-07-02 05:49:38

The ratio of the energy to attain orbit to that to reach the same height is: (m*g*h+0.5mv^2)/ m*g*h or approximately a factor of 32. To take SS1 from 100kms to ISS orbit at 400kms would require about 36 times more energy.
And after suborbital tourism will come suborbital transportation, fast worldwide point to point services. Yes it will be a long time (2020+) before orbital tourism literally takes off other than for the super rich.

You forget Newton's millstone, the Tiokovski equation: to push SS1 up to orbital velocity might not take an insane amount of fuel, but pushing that fuel does. As the target velocity increases, the fuel mass increases exponentially, especially with such a low specific impulse fuel.

An orbital model of SS1, lets say tripple the mass for a heat shield, power, and OMS systems - mated to a single-stage orbital "rubber rocket" booster - would not fit on a 747 jumbo jet.

cjchandler · 2006-07-02 06:04:45

I agree, the hype over spaceshipone is a bit over done. It only needed 1300 m/s de;lta v and yet it was almost 66% fuel by weight. With good liquid fuel rockets only 25-30% would need to be fuel. Yet people don't seem to understand that suborbital is with a capital SUB.

GCNRevenger · 2006-07-02 06:11:14

Soyuz flights are not tourism any more than there is a tourist industry for climbers to scale Everest, only handfulls of people will do it, and even with a Russian markup of ten million a flight that still really isn't very much money. To make a really good small reuseable orbital vehicle will cost several billions for Russia to make or $10-15Bn for us.

This business about worldwide suborbital delivery of precious cargo is silly too, for the vehicle to really cut travel time it would have to be on "standby" around the clock, and able to launch very quickly, which I think would be hard to do. I also think the cost and low demand for such a thing would pretty much preclude anyone making any money off it.

GCNRevenger · 2006-07-02 06:34:06

Oh, and then there are "political" issues with suborbital freight...

1: If you have to launch in a hurry, how does the destination country know that you are not a hypersonic ballistic missile reentry vehicle? With so little warning and all.

2: If you crash at multiple mach numbers into a populated area, the explosion will be as big or larger then the USAF's "MOAB" superbomb. Who pays for that? And can you imagine the insurance?

cIclops · 2006-07-02 14:00:12

You forget Newton's millstone, the Tiokovski equation: to push SS1 up to orbital velocity might not take an insane amount of fuel, but pushing that fuel does. As the target velocity increases, the fuel mass increases exponentially, especially with such a low specific impulse fuel.
An orbital model of SS1, lets say tripple the mass for a heat shield, power, and OMS systems - mated to a single-stage orbital "rubber rocket" booster - would not fit on a 747 jumbo jet.

Opps so I have!

Okay so SS1 would also need to lift the mass of fuel required to accelerate it to orbital speed, say 8000m/sec. As SS1 uses a N2O/HTPB motor with 2500m/sec, it requires an initial mass of m*e^(8000/2500) = 24m, eg 23 times its own weight in fuel. Doing the math behind the screen now makes it a factor of 128 in energy terms, yes ok just another factor of 4

And as you say that also ignores the need to carry a heatshield and the extra structure to support all that mass ... yikes.

cIclops · 2006-07-02 14:21:15

Soyuz flights are not tourism any more than there is a tourist industry for climbers to scale Everest, only handfulls of people will do it, and even with a Russian markup of ten million a flight that still really isn't very much money. To make a really good small reuseable orbital vehicle will cost several billions for Russia to make or $10-15Bn for us.

You might be interested in checking out these tables in particular this one that gives the names of people reaching the summit of Everest between May 15 and May 27 2004 .. a total of 167.

Nowadays people are not only climbing Everest they are also traveling to both poles .. the so called "Three poles of the Earth" tour - a very expensive holiday!

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