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Comment by pqdbr | Hacker News Reader

I don't understand this: article states it will drift as space debris for 55 years (!) before reentering the atmosphere? Why isn't this done immediately by just lowering it's orbit even further and letting it burn?

> The final steps included carefully lowering the satellite's orbit to decrease the risk of collisions and ensuring that all energy sources, such as fuel and batteries, are depleted to prevent the satellite from accidentally turning back on or creating debris. As Landsat 7 begins this decommissioned phase, it will drift silently in orbit for about 55 years before reentering Earth’s atmosphere.

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> "Why isn't this done immediately by just lowering it's orbit even further and letting it burn?"

It'd take a very significant and expensive amount of fuel to "just lower" the orbit! From its 700 km orbit, it'd cost (by my estimate) roughly 300 m/s, or on the order of 10% of entire satellite mass, to perform this lowering burn.

It's not at all standard practice to deliberately dispose of satellites this way (SpaceX is a major outlier), and wasn't even on the radar in the 1990's, when this satellite was being built.

(Here's an anchoring point: the projected cost for the propulsion to "just" deorbit the International Space Station, at the end of its operating life, is $1.5 billion [0]).

[0] https://spacepolicyonline.com/news/nasa-iss-deorbit-vehicle-...

> (Here's an anchoring point: the projected cost for the propulsion to "just" deorbit the International Space Station, at the end of its operating life, is $1.5 billion [0]).

That's under 2% of the total cost, that's not too much, if you compare it to the rest of the TCO, and not how beneficial would it be.

Should use the ISS as the base mass for a EM launcher. Seems nuts to waste so much on that existing potential energy.

ISS is in a bad orbit for this sort of thing: halfway between the best orbit for Baikonur and the best orbit for Kennedy, it was a compromise which was okay because it wasn't getting that much traffic, so the penalty didn't amount to much at the scale of the budget. Using it as an orbital way-station will end up paying that compromise penalty a whole lot of times on all the launches up to the station, driving up the total value of the orbital penalty. If you are doing something big enough in space that you can afford to keep the ISS in operation (1) then you are probably better off building your own platform in the right orbit for your launch site. (2)

Also, repeated dockings and undockings (as you assemble the mass driver and then use it) will ruin any microgravity experiments you might want to run, so you can't really combine "base station for deep space exploration" and "science lab" missions, you really need the station to be focused on one or the other.

1: The main problem ISS has is political, not technological. By design you need the US and Russia to cooperate to keep it operating, and that made a lot of sense in the 1990s, and has fallen apart over the past decade.

2: Orbital plane changes- to move ISS to the right orbit for a specific launch site- are hideously expensive in LEO. GEO satellites often find it cheaper to raise their apogee out to near the moon, make the necessary plane change way up high, and then drop the apogee again when they get to perigee, rather than make the plane changes in LEO. (ISS can't do that.)

It's in the ideal orbit for Baikonur. It's much, much easier for a low-latitude launch site to reach a high-inclination orbit than vice versa. This is especially true for Baikonur, where the available inclinations are restricted by human habitation and foreign countries downrange. Hence the minimum inclination is 51.6 degrees (which is where the ISS is) despite the launch pads being at 46 degrees latitude.

You are correct, I had remembered the details wrong- ISS and Mir and Salyut 7 all have the same orbital inclination, so that's clearly the best orbit for Baikonur. So if you were doing your mass launches from Baikonur you would not pay much of a penalty. From KSC, though, you'd almost certainly want a lower inclination to get more payload up.

Really, you pay the same penalty launching to 51.6 degrees regardless of whether it's Baikonur or KSC. But you're totally right, you can do even better by launching to lower inclinations out of KSC, which can go down to 28.6 degrees.

1.5 billion??? if starship from space x is ready by the end of service. can we make it cheaper using starship? using robot arm or just push it to designated landing point with starship

This is basically what they’re doing; most of the cost is for SpaceX to modify one of their existing vehicles into the USDV. You probably underestimate how much energy is needed to deorbit ISS.

I wonder what the real costs are and what is taken as profit

still better than competition

It seems to be a common misconception that lowering an object's orbit is much easier than raising it. I guess because it feels like it is just floating up there and gravity can do most of the work to pull it down if you give it a little nudge. In reality the energy required to lower the orbit is about the same as the energy required to raise it. In both cases you need to change the orbital velocity.

then just push it out of orbit

> just

You keep using that word. As another response said, you seem to underestimate how much energy is needed to deorbit ISS. It has a mass of 450,000 kg and is moving at nearly 8km per second. There is no 'just' here.

> It's not at all standard practice to deliberately dispose of satellites this way (SpaceX is a major outlier), and wasn't even on the radar in the 1990's, when this satellite was being built.

tbf it is now a standard practice (quite literally: it's part of ISO24113) for satellites in LEO to lower the orbit to allow reentry via natural orbital decay within 5 years or less (recently reduced from 25 years or less). Your average CubeSat launched into the lower reaches achieves this naturally through atmospheric drag without propulsion, but anyone sticking their satellite at 700km needs propulsion and sufficient total impulse to be able to conduct a deorbiting mission at end of life.

But yeah, certainly wasn't in the 1990s when congestion of LEO wasn't a consideration

you would need to carry enough fuel on board to get rid of most of the velocity obtained during orbital insertion. That is lots of fuel

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