[sebzim4500]

It's not groundbreaking but it's important. They are demonstrating in orbit relight capability of the raptor engines. This is an absolute requirement before they can put it fully into orbit because losing control of a Starship in low earth orbit would be catastrophic.

[lysace]

> because losing control of a Starship in low earth orbit would be catastrophic

Why? Remote detonation wouldn't work in that case?

[perihelions]

Remote termination is something they can do in the early boost phase, when there is a defined hazard zone over a depopulated patch of ocean. It doesn't cause the rocket to disappear; its effect is to disable the engines, end uncontrolled acceleration, and break the booster apart into small pieces—all of which will still fall to the ground (ocean) as debris.

If you did this to a Starship in orbit, you'd likely have large chunks of steel reentering and reaching the ground intact.

[lysace]

If I understand you correctly: So you'd have to do it over unpopulated/depopulated areas, which is impossible to guarantee when you are zooming around the globe at very high speeds. Thanks for explaining.

[mcswell]

"...all of which will still fall to the ground (ocean) as debris..." After it's been flying in orbit for awhile, where it could in theory hit something else.

As you say, the other part of it--and probably more important--is that if it's turned into orbiting pieces, there's no control over where it lands. Some of it could easily land on the ground rather than the ocean, who knows where. That of course has happened with other satellites and their final stage rockets in the past (notably by the Chinese), but Starship is bigger, and therefore the pieces that hit the ground could be bigger. By launching it sub-orbital for now, and turning off the engines so it lands in the middle of the Indian Ocean, the risks of both orbital debris and unknown ground landing points are avoided.

[jpk]

If the object is already in orbit, the debris from an FTS activation would also mostly be left in orbit, which isn't great. They really need to demonstrate the ability to de-orbit the vehicle before putting into orbit.

[stetrain]

Generally that isn't done for a vehicle in orbit, since the distribution of debris in orbits used by other spacecraft would be significant.

A Starship second stage stranded in orbit would be a problem because detonation would cause a bunch of orbital debris, but simply waiting for natural re-entry would result in an unpredictable landing location that could result in large debris reaching populated areas.

Reliable, controlled re-entry to a targeted location is very important for Starship to be an operational launch system.

[inglor_cz]

It would work, all too well. Especially if the speed was just slightly suborbital. Rain of steel over a random spot (or, rather, a trace) on the Earth's surface. You may be lucky and that trace might cross a desolate ocean; or you may not be lucky, and some Asian megalopolis with 25 million people may be below.

[cryptonector]

Detonation in orbit would cause garbage in orbit that could destroy many satellites. It is absolutely not permitted.

[lysace]

That makes a lot of sense.

[valine]

Detonating something in orbit could trigger Kessler's Syndrome.

[JumpCrisscross]

> Detonating something in orbit could trigger Kessler's Syndrome

Unlikely in general, no at LEO and definitely not at the suborbital velocities IFT-6 contemplates.

[kibwen]

Even at suborbital velocities, putting debris into the path of an existing satellite that is traveling at orbital velocity is enough to trigger a cascade.

[Dylan16807]

The chance anything hits fragments within the next hour or two is not very high.

[JumpCrisscross]

Collision, yes, cascade no.

[kibwen]

No. An object in orbit colliding with anything threatens to create debris in orbit. Debris in orbit collides with other objects in orbit, creating debris in orbit. That's a cascade.

[valine]

LEO is the exact place you need to be careful. Higher orbits have more space and have fewer satellites overall so it's less of a concern.

Obviously not a problem for IFT6 since it's sub-orbital, but the original comment was about why we need a deorbit burn rather than just triggering the flight abort system.

[JumpCrisscross]

> LEO is the exact place you need to be careful. Higher orbits have more space and have fewer satellites overall so it's less of a concern

No. In LEO orbits degrade in single-digit years at most. There is no known solution for rendering an orbit in LEO inaccessible with a Kessler cascade—the best you can do is blind an area with repeated ASAT fire.

In higher orbits debris last longer. That makes cascades possible, though again it only denies a limited area and requires almost active effort.

[gridspy]

At least in LEO you need to keep expending DeltaV to keep stuff in orbit. Trace atmosphere slows everything down and would eventually clean LEO at 500km of relevant junk in about 25 years depending on altitude.

https://space.stackexchange.com/a/55995

[pantalaimon]

but lower orbits also decay quickly.

If you have debris in geostationary orbit, it will stay there basically forever whereas in low earth orbit it will burn up within a few years at worst.