idea for getting into space cheaply

prankster

helloo! i have an idea that i've been thinking of and i'd like to get some opinion of its validity.

imagine 4 hydrogen balloons (like those used to carry weather instruments), arranged in a square with one balloon on each corner. imagine in the middle, suspended by cables below the balloons is a rocket. the rocket will have multiple stages, 1st being a lower power stage, followed by maximum power stage, and finally a long burn medium power stage.

situation is as follows: release the apparatus , and the balloons carry the unit to ~90,000'. at that point the balloons are nearing their critical bursting point. the 1st lower power stage activates to creep the rocket up to the center of the balloons ( 3 stabilizer rockets at the top of the main rocket handle the rockets angle at this point) meanwhile the lines are severed.

once the rocket clears the balloons, the main engine is ignited carrying the rocket further into earth orbit. when the 3rd stage ignites, the rocket is maneuvered into a roll and a stable orbit ensues.

the actual rocket would not have to be so heavy, because the main obstacle of overcoming the earth's gravity is done by the balloons. so i pose the following questions:

1) is this feasible?
2) is this scalable?
3) at what altitude does the earths gravitational 9.8m/s^2 reduce to an advantage? (at this altitude of 90,000' i calculate 9.7368m/s^2)


thanks! ive had this idea on my mind for quite a while, so any feedback (including telling me its rubbish) will be helpful!

Mech_Engineer

Many people have asked about a floating rocket platform at ~100,000 feet to help save in fuel, but it doesn't really help at all.

To get into orbit, you need specific energy in the form of velocity, not height. The potential energy at 90,000ft pales in comparison to the specific energy required to achieve orbit (let alone escape velocity). And for the record, gravitational pull at 90,000 ft is basically the same as at sea level.

EDIT:
Just some numbers to back it up:

At an altitude of 90,000ft, your specific energy due to the gravitational field is about 0.27 MJ/kg (none of which is useful for velocity, except perhaps to help avoid some small amount of atmospheric drag). The specific energy required to achieve orbit is about 30 MJ/kg. So you can see adding height has not helped at all.

chroot

Low-earth orbits are typically about 200 miles above the earth's surface. Even if your balloons could carry your craft to 90,000 feet (17 miles), you're not going to accomplish much as far as altitude is concerned.

Also, the biggest problem with getting into orbit is not gaining altitude, it is gaining tangential velocity. You need to get above most of the atmosphere in order to reduce drag and obtain a stable orbit, but you also need to be moving at about 17,000 mph tangent to the earth's surface.

The "obstacle of overcoming gravity" is not lessened by your idea. The earth's gravity is not even 1% weaker at 90,000 ft than at sea level, since 90,000 ft is less than 1% of the earth's radius. "Overcoming gravity" has nothing to do with altitude, really, just velocity. The geographic locations used to launch spacecraft are invariably chosen near the equator, because that provides about 1,000 mph of "free" tangential velocity due to the earth's rotation. If altitude were the problem, we'd be trying to launch them off the top of mountains, instead.

Your idea reduces the altitude burden by about 8%, but does nothing to solve the problem of obtaining sufficient tangential velocity. As such, I think it's interesting, but ultimately not useful.

- Warren

mgb_phys

It has a few other advantages
It lets you 'launch' from the best point on Earth for the orbit you require without worrying about where you can build a space center.
You can launch in any weather, there isn't much weather >50,000ft to mess you up.
It's easier to build a rocket that only has to operate in very sparse atmosphere than one that has to manage both thick sea level and sparse high altitude conditions.
Steering the rocket is also much easier, at altitude you don't need the high degree of rapid directional control that is needed to get it past the launch tower and clear of surface winds.

This is already being done with the Pegasus system - with a rocket released from under a converted airliner, Virgin Atlantic is also looking at a launch from it's high altitude test aircraft.

FredGarvin

The winds aloft at 50,000 ft + are usually horrendous. They're not bad if you are already launched and going supersonic by that point, but on a floating dock, they would be horrible.

Mech_Engineer

The jetstream is from about 30,000-50,000 ft, but there really aren't any winds at 90,000ft. Weather balloons at 100,000ft are able to loiter in a relatively small area for several hours, but if one spends too much time in the jetstream you'll cover hundrends of miles.

More important than that, how big would these 4 balloons have to be to lift a multiple ton rocket up to 90,000 ft? We designed a 5-lb weather balloon payload in college, and the size of them is pretty impressive at max altitude. Lifting a 50-ton rocket (not even including the weight of the platform itself) would require balloons that displaced a total of 1.6*10^6 m^3 of air at an altitude of 90,000ft, more than 8 times the volume of the Hindenburg. An altitude of 100,000 ft would require 2.6*10^6 m^3 total displacement.

Mech_Engineer

That's the argument for sea-based launch platforms, and its a pretty good one. This floating platform would probably have to be launched from a sea-based platform, and then you would have to chase it back down. Altitude and attitude control would be a real problem.

Not if the weather is bad when you're getting ready to launch the platform. The weather conditions might have to be even more stringent for a platform that is held aloft by 4 gigantic balloons.

This might be true, although I wonder if the largest forces at work on a rocket are really aerodynamic or just acceleration in general.

Edit- This depends on the speed of the rocket and when it is during the flight. Most rockets experience Max-Q due to aero drag at about 50,000ft or so.

How the heck are you going to steer the launch platform around in any kind of surface winds?? Just release it and hope it stays level?

I think the real problem is just that rockets capable of reaching orbit with an appreciable payload are BIG, and can't really be carried by an aircraft (especially not in a horizontal orientation).

mgb_phys

I was thinking about a aircraft launched rocket - not the crazy balloon idea.

You can carry an (empty) space shuttle on the back of an airliner.

The pegasus is a pretty successful system - I was at the launch of an Infrared observatory by it 10years ago.
According to their site they can put 450kg into LEO, only about 1/10 of the capacity of a Delta or Ariane but a lot cheaper!
You probably aren't going to use it for a GSO communcations sat but great for GPS, sat-phone etc in LEO, especially because you are so flexible in the orbit window.

They claim the biggest cost advantage is that they don't need a steerable rocket motor.
To control a rocket's attitude at launch you need a lot of torque to overcome any wind or imbalance, that means a seriously complex vectorable rocket motor.
The pegasus can make much more gentle course corrections with just aerodynamics.
i suppose this is just because they have much more time and space to play with to make corrections because there is nothing around them.

Q_Goest

The sea based concept has already been done, it's called "Sea Launch". Prime is Boeing. They use a Russian rocket for low cost, and they've done ok, but had a few missed launches and my understanding is they're in bad shape right now. The rocket launching industry is extremely competitive with Lockheed Martin and Boeing merging now to create the United Launch Alliance to help reduce costs. Pegasus is of course, only for very small satellites, so small they can't even be counted.

I'd agree with Mech Eng, the size of the balloon is prohibitive. There have been companies such as Skylifter that have tried to use balloons for very heavy lifting, and they really aren't economical. The problems with operating a balloon that large include enormous costs for helium and helium clean up, ground facilities, and I suspect many other issues I'm not aware of. It's just a very impractical way of lifting a large payload.

D H

You are ignoring the rocket equation.

The same goes for you, Warren.

It's not such a crazy idea, and it is not a new idea at all. This idea is older than me! http://en.wikipedia.org/wiki/Rockoon

The fuel savings are surprisingly huge. Thanks to the rocket equation alone, even a tiny reduction in the energy (kinetic+potential) that must be supplied to the payload can correspond to a significant reduction in fuel costs. Add in the facts that (a) the rocket is not plowing through the lower atmosphere and (b) rockets work quite a bit better in vacuum and voila! 20-25% reduction in fuel costs are easily achieved by launching at extreme altitude.

So why don't we do this?

• If the rocket fails, where it will fall is a bit problematic.
• If the rocket succeeds, whether it will end up in the desired orbit is a bit problematic.

Q_Goest

Hi mgb,
Actually, the Delta, Atlas and Ariane rockets can put at least 10 times that much into geosynchronous or geostationary orbit. They'll put about 50 to 100 times that into LEO. Pegasus certainly takes advantage of the aircraft launch platform. They have a good thing going for extremely small payloads, but I wouldn't compare them to the other rockets. They're just not in the same category.

mgb_phys

Not sure height buys you very much.

Some velocity helps but the fraction of fuel you need is still proportional to e^-dV
if you need dV of 10km/s for Leo then adding 0.25km/s for an airliner isn't going to do much,
the optimum first stage drop velocity is something like 1/3 of the final velocity.

Mech_Engineer

Oh I'm quite aware that it isn't a new idea, but it still definitely isn't a practical or economical option.

Well, a 20-25% reduction in fuel requirements sounds good, but would it result in a 20-25% reduction in total cost? Not even close, it would overall probably be MORE expensive considering the cost of Helium, plus the launch platform itself and all of the stuff that goes along with it. Fuel is cheap in comparison!

Those are a couple of problems, but don't forget some of the most important ones-

• As I pointed out, the total volume of helium required to lift a rocket of a "useful" weight to a "useful" altitude is definitely prohibitive. It looks to me that based on my previous volume estimates and estimated cost of Helium per cubic meter, you're looking at about $10 million in Helium alone per launch (if we can even keep up with that kind of demand...), and that's only for a 50 ton rocket which isn't all THAT big.
• Dragging a large rocket to altitude will take time, advanced equipment, and a lot more than a few cables with a balloon.
• What happens if the platform drifts over land? What if you need to abort launch at 90,000 feet? What if a balloon bursts and the whole thing comes down? Attitude control of the platform itself? Recovery of the platform?
• Acceptable launch conditions would probably end up being more stringent than a ground-based rocket, due to the size of balloons required. It's pretty calm at 90,000 ft, but the whole platform would have to be assembled and filled on the ground (or water) first.

mugaliens

Good analysis, and the fact it only helps out by about 1% with boatloads of additional cost and complexity is the reason it's not done.

Our space center is already built.

Not really a factor when you can simply delay launch until the weather has passed.

Not really, as a surface-launched rocket is quickly past more of the forces. The greatest force on the Shuttle occurs as it's passing mach. After that, the rapidly thinning atmosphere results in quickly reduced forces.

Not really. A rocket requires active steering throughout its flight regime.

Altitude is but one benefit of the Pegasus system. Velocity is the main benefit, however.

The Pegasus system is also extremely costly in terms of $/kg to LEO. It's only useful when the payload is small enough that using larger launch platforms is a more expensive option.

Greg B

Hello,
This discussion has been held in many different forums and the answers are generally
obvious because of the dictations of the physics involved.

There was even an engineering study on the subject.

Although there are gains do to reduction in drag ,The biggest predominant factor is
the energy required to achieve orbital velocity.

Buts lets make it even simpler ,here is the economics of it.
The pegasus vehicle cost is $30,474 per kg
The STS cost is $10,416 per kg
The Ariane 5 cost is $9,167 per kg
The proton cost is $4,297 per kg

Vehicle costs are 100 to 1000 to 1 in comparison to the cost of fuel so the economy
of size is the biggest factor in cost.

Which essentially eliminates balloon launching and limits aircraft launching
to small NIRTS payloads.

Greg

Jeremy.space

I have a question that relates to this one.
If we got a balloon to reach just over 120,000ft with a rocket attached to it.
Is it possible to get the rocket into a geosynchronous it will have a payload consisting of no more then 1.5kg?

enigma

Hi Jeremy,

That depends on the size of the rocket. Look into the "ideal rocket equation" and "Hohmann transfers". Give a shot with the math, and if you have problems, feel free to post in the homework help section of the forum.