Sophisticated Balloons Could Help Steer Spacecraft

coondoggie writes "Getting spacecraft traveling at hypersonic speeds to slow down and land or achieve a particular orbit on a dime is no easy feat. But researchers are developing a tool that will let engineers model and ultimately build advanced flight control systems that meld balloon and parachute technologies known as a ballute (BALLoon-parachUTE). Basically a ballute is a large, inflatable device that takes advantage of atmospheric drag to decelerate and capture a spacecraft into orbit around a planet, according to NASA who is funding Global Aerospace to build such a tool."

Re:Old tech?

[interiot]

Yup, it was invented in 1958 [parachutehistory.com], and was used on the Gemini back-up ejection seat, and is used on the Mk-82 unguided gravity bomb.

Re:Typo in summary

[Sopor42]

Oh it [wiktionary.org] is, is it Mr AC?

Problems with atmosphere breaking

[khallow]

The key problem with atmospheric braking is heat dissipation. Craft in orbit have considerable energy (since they have orbital velocities of around 7.5 km/s or more) while craft returning from the Moon or Mars have far greater velocities (the Apollo capsules returning from the Moon had velocity of roughly 11 km/s, which is double the kinetic energy per kilogram of a low Earth orbit satellite). Entering orbit around a gas giant (like Neptune) will require even velocity dissipation. If you and everything on your spacecraft were indestructable, you could just dive straight in. In practice, since spacecraft aren't indestructible and payloads (eg, living humans) are somewhat fragile, you need to decelerate at a much more gradual pace. As it turns out, the sooner you can start deceleration, the better. The key way to decelerate early is to increase the cross-section area of the vehicle relative to its mass. This also has the advantage of distributing the heat load from atmospheric braking across a wider area and reduces the overall temperature of the vehicle. This reduces the complexity of the structures used to protect the vehicle from atmospheric heating (called "thermal protection systems" or TPS).

Capsules like Soyuz or Apollo have the highest mass per cross-section area and hence have high heating loads and decelerations. The Shuttle has pretty high heating loads as well. If it had been made considerably "fluffier", it wouldn't need the special tiles for its TPS.

Ballutes are cheap ways to greatly increase the cross-sectional area of the vehicle. For a fictional example of a ballute, the film 2010 portrays the Soviet spaceship, Leonov using one as it aerobrakes to slow down enough to orbit around Jupiter. Technically, in this case, it is aerocapture. This is aerobraking with only one pass through atmosphere. The usual process involves many passes through atmosphere, shedding some velocity on each pass.

The innovation in this article is the ability to control a ballute which has some lift. There are two possible uses that I can think of, off the top of my head. First, it can be used to steer the vehicle so that more of its path is in the less dense high atmosphere. In other words, we can steer to some degree the trajectory so that we get better deceleration and heating loads. Second, aerocapture is very hard. The key problem is that any changes in the atmosphere will change the trajectory, possibly enough to make the attempt unsurvivable. Even if the vehicle isn't in danger, small differences in the atmosphere or the vehicle's reentry trajectory mean the vehicle may end up on a different trajectory. If it is landing, it may end up far away from the desired landing spot. Ability to steer reduces the uncertainty of aerocapture and provides some valuable margin of error for a spacecraft.

Re:MAGIC BALLOONS

[LandKurt]

The smaller and denser an object is the worse the heat load is on re-entry. Using a ballute to increase the surface area means there is less need for high tech fragile ceramic tiles. Another way to look at it is that the greater area means there is more force to slow down the spacecraft before it gets into denser levels of the atmosphere.

Re:Old tech?

[EdZ]

Ballute assisted re-entry has been a staple of the Gundam franchise for quite a while, along with wave-rider [wikipedia.org] airfoils and O'Neill cylinder [wikipedia.org] colonies. Some of the science behind it is rather good, though somewhat offset by the idea that giant robots make everything work better.

Re:Yet another score by the late Arthur C. Clark

[Anonymous Coward]

Heinlein had a few degrees in that area- IIRC.

Nope - you must be thinking of someone else. Heinlein was a graduate of the Naval Academy and a dropout from UCLA.

Re:MAGIC BALLOONS

[Nyeerrmm]

This is being used for aerobraking and aerocapture, not entry/re-entry. The idea is that it flys through the upper reaches of the atmosphere to slow it down and send it into some kind of closed orbit about the target body. Not nearly as much of a heating issue, particularly if you're talking about Mars which has a much less dense atmosphere.

No real reason to use it for re-entry since a Viking-style Mach-2 chute, or one of the new-fangled Mach-3 chutes will do the job already.