Debris Intercept Towers

Using launch loop "dynamic structure" technology

Some believe 40 km suborbital loops can support a launch tower and accelerator for a smaller conventional rocket, avoiding a few hundred meters per second of velocity lost to air drag, but that isn't a huge fraction of 7.7 km/s orbital velocity. Avoiding a 300 m/s loss compared to a 3000 m/s rocket exhaust velocity is a 10% mass improvement - at the cost of lifting an entire multistage rocket and its launch support structure (launch tower, fuel tanks, flame duct, etc.) into the sky.

Stratolaunch implies that the launch support structure for a small rocket has the mass of 747 aircraft; 340 tonnes of aircraft for a 250 tonne passenger rocket. That is useful, not because of the launch mass saved, but because the Stratolaunch aircraft can travel far out to sea and launch to any azimuth, thus reaching any orbital plane, without worries about dropping launch-abort rocket stages onto inhabited areas.

For comparison, a SpaceX full thrust Falcon 9 has a launch mass of 550 tonnes to deliver a vehicle mass of 23 tonnes to LEO. If scaled down linearly to a payload 1 tonne-to-LEO (it doesn't, drag is square to cube), that might be 22 tonnes of rocket (scaled by down by 1.1 for lower drag) and perhaps 20 tonnes of rocket launch support structure. 43 tonnes total - a considerable mass to support.

That said, the notion inspires my favorite phrase, which I hope to hear from many of you, backed by physics and calculation:

That won't work, but this will!

An important, expensive, and neglected space mission is de-orbiting space debris from Low Earth Orbit. I include the spent upper stages used to loft satellites into high orbits, like the Russian Molniya comsats; those derelict upper stages come bombing through LEO at high speed, threaten enormously expensive assets like ISS.

Deorbiting an object means dropping the perigee of its orbit down into the atmosphere, and the best way to do that is to reduce apogee velocity. The second best way to do that is to reduce perigee velocity so much that apogee becomes the new, lower perigee. That requires delivering a lot more delta V, but will eventually bring the object down.

Instead of using a suborbital loop supporting a big chemical rocket, it can instead support a velocity transformer track (as below) to magnetically launch many small (20 kg?) 25 gee vehicles into suborbital retrograde ballistic trajectories. 20 gees and 40 km is 3840 m/s + 430 m/s drag loss (WAG); if the exit is at a 60 degree angle, that is 3320 m/s vertical velocity, an apogee of 900 km, and a retrograde velocity of 1.28 km/s.

After launch, adjust the velocity with laser ablation thrust, from a laser platform suspended under the loop.

What's that good for? Launching canisters of expanding foam precisely in front of a derelict space object, slowing it down and deorbiting it after enough impacts. All earth-orbiting objects cross the equator twice per orbit. One of those crossings must be low enough for this kludge to reach it - a faster launcher will be needed for higher objects.

debris.ods libreoffice spreadsheet ( gate:keithl/launchloop/. )