SpaceX Dragon fires thrusters to boost ISS orbit for the 1st time

[Admin]

SpaceX's Dragon performed an orbital boost maneuver for the ISS; a first for the spacecraft, and a small step toward the space station's ultimate doom.

SpaceX Dragon fires thrusters to boost ISS orbit for the 1st time : Read more

 

[M.S.]

"The International Space Station is going a just tiny bit faster today, after receiving an orbital boost from SpaceX's Dragon spacecraft."

I believe the ISS will l be actually going a just tiny bit slower today, as the purpose of the orbital boost was to rise the ISS into a bit higher orbit, and higher orbit means lower orbital speed.

 

[Unclear Engineer]

Not quite so easy to explain, but the speed is faster, where the boost occurred.

I did not look up the actual parameters of the boost. But, generally, the boost should occur at the high point (apogee) of the orbit, and increase speed in the direction of the orbit. That will bring up the altitude of the low point of the orbit (perigee). Because the speed is highest at the low point, M.S. is correct that the average speed of an orbit around the Earth would be slower after the boost. But, it will be going faster than it was previously going at the high point. It will be going slower at the lowest point of the new orbit, compared to the unboosted orbit.

 

[Aramis]

Cygnus has already reboost the ISS

https://www.space.com/space-station-cygnus-orbit-reboost-success

Northrop Grumman's Cygnus cargo ship boosts International Space Station's orbit​

 

[Unclear Engineer]

Yes, so has the Russian Progress supply ship.

This is another one of those headlines that seems to imply something more special than it actually is. This isn't the first time that the ISS orbit has been boosted - that is fairly routine. It is the first time that a SpaceX rocket has been used to do it. And, that is why it is being done with the Dragon capsule, so that SpaceX can get the data it wants to design a purpose-built rocket to deorbit the ISS.

 

[Classical Motion]

It wouldn’t surprise me that if today, all they do is punch in the new altitude needed. And then let sensors, software and thrusters complete the task. Getting a feedback feel, for future tasks. Live feedback control, not pre-programmed control.

An experience catalog. Experience programming.

 

[Unclear Engineer]

They might automate the boost thrust sequence. But, given the issues with stuck valves, thruster malfunctions, etc, on multiple ships, recently, I expect that there is going to be a human watching the machines with the ability to stop the rocket motors if things don't seen to stay within specs.

 

[Classical Motion]

I did a little process programming about 25 yrs. ago. Any error or out of parameter condition is handled by software. It’s much quicker and the correct procedure can be assured. Hopefully preventing or limiting damage.

But any new hardware or software change needs to be watched like a first child bike ride. And with space vehicles I would want someone watching a monitor all the time. Bridge duty.

But I have no idea of what goes on up there.

And I never had a chance to work with learning software. I probably assume too much.

 

[M.S.]

Not quite so easy to explain, but the speed is faster, where the boost occurred.

I did not look up the actual parameters of the boost. But, generally, the boost should occur at the high point (apogee) of the orbit, and increase speed in the direction of the orbit. That will bring up the altitude of the low point of the orbit (perigee). Because the speed is highest at the low point, M.S. is correct that the average speed of an orbit around the Earth would be slower after the boost. But, it will be going faster than it was previously going at the high point. It will be going slower at the lowest point of the new orbit, compared to the unboosted orbit.

I don't know the parameters of the new orbit either, but the boost increased the total (kinetic+potential) energy of the the ISS.
Since the total energy is determined by the semi-major axis of the orbit, higher total energy means larger semi-major axis, which in turn means lower average speed. The question is whether the boost changed the eccentricity of the orbit. If the eccentricity did not change, then both perigee and apogee have larger values, and therefore both perigee and apogee speeds are lower than before the boost. But if the eccentricity increased, it might well be that perigee speed is now larger than before, and apogee speed much lower that before.

 

[Unclear Engineer]

The goal is to get the ISS out of the drag-inducing upper atmosphere at the lowest point of its orbit, so the most "bang for the buck" it to raise the perigee. And that means increasing the speed at the apogee.

But, you are correct that will create a lower average speed over the entire orbit.

Still, you are picking nits between increasing speed at the apogee vs decreasing average orbital speed when you do that.

Most people do not understand orbital mechanics. So, the article just said the thrust increased the speed to boost the orbit. People might have otherwise thought that the thrust would just point "up" (radially away from the Earth) to boost the orbit. But, that would have increased the eccentricity, and, depending on where applied, could be counter-productive for reducing drag effect per orbit.