There's a thread over in space policy for discussion of how the current geopolitical situation effects ISS. Go there to discuss that.
https://spaceflightnow.com/2022/02/21/northrop-grumman-delivers-cargo-and-new-reboost-capability-to-space-station/This Cygnus mission will also debut a new capability to reboost the altitude of the space station, a service that has been exclusively provided by Russia since the retirement of the space shuttle in 2011.
“This Cygnus vehicle has been modified to provide a capability to reboot ISS, so to use some of its propellants in the vehicle itself,” Contella said. “We’ve done a test prior to this with Cygnus, but this will be our first real use of this capability to actually reboost the station. And it gives us another way to do so, in addition to the Russian thrusters or the Russian Progress cargo spacecraft capabilities.”
The Northrop Grumman cargo ship has a gimbaled delta velocity engine to make the reboost maneuver possible, officials said.
So if the Russians were no longer a part of the ISS partnership
(for reasons which will go unspoken), and Cygnus was the only means of reboosting the station, what would that entail? Is a Cygnus flight and boost twice a year enough to keep the station at altitude, or would more be required? Or perhaps a dedicated boosting vehicle based on Cygnus?
This will also be a good place to discuss that first reboost, when it happens.
CMG Desat is a bigger question.
CMG Desat is a bigger question.
It was alleged that using the solar panels, aligned to produce max drag, might be a way to desaturate these... I don't know if that's a reasonable idea or not.
The bigger problem would be that the service module for the station is Russian, and unless Russia wants to give up half it's station they will likely remain.
CMG Desat is a bigger question.
Control Moment Gyro (CMG) (took me a while to remember that acronym.)
This is a good point.
I imagine Cygnus could help with that too, but don't have a clue how often desat is needed.
Maybe it would be too frequent and require too much propellant?
CMG Desat is a bigger question.
If you want to make a thread on CMG Desat, go right ahead. I'll follow it.
There’s also the option of using gravity gradient. The station can be put into a gravity gradient stable attitude if there’s a problem.
Gravity gradient, together with drag, has been demonstrated before on ISS to enable Zero Propulsion Maneuvers.
In this case, you still need reboost capability. Which Cygnus can provide.
The ZPM concept is based on developing a special attitude trajectory to accomplish the desired rotational state transition without exceeding CMG capability, i.e. peak momentum and torque magnitude. The trajectory is shaped in a manner that takes advantage of the nonlinear system dynamics. The key is to coordinate and modulate attitude-dependent environmental torques. Coordination is accomplished by varying the maneuver rate, i.e. speeding up or slowing down. Modulation is achieved by commanding attitude excursions. This is similar to the way a sailboat would tack against the wind. In this analogy, the CMGs represent the ship’s “rudder,” the gravity gradient torque is the “wind,” while aerodynamic torque is the “ocean drag.” This is shown in Figure 8. For example, an eigenaxis maneuver is kinematically the shortest path between two orientations. For the attitude controller system to follow the eigenaxis, the nonlinear system dynamics must be overcome, thereby increasing the “cost” of the maneuver. By considering a kinematically longer path and increasing the time to perform the maneuver, path dependence of system dynamics can be exploited to lower the “cost”. This allows spacecraft that use momentum storage devices for attitude control, such as the ISS, to perform large angle attitude maneuvers non-propulsively.
https://ntrs.nasa.gov/citations/20080009592
Scott Manley's recent YouTube video on using Cygnus for boosting ISS and other things related to war.
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If Cygnus (or Dragon 2 or Starliner for that matter) was launched with no Science payload at all, could it carry more fuel for attitude control / orbit boost? I assume that the propellant tanks get topped off for every launch, but maybe not if they are compromising for up-mass to the space station. If they are full I wonder how much of an engineering challenge it would be to add and connect a reserve tank in the un-pressurized cargo section?
If Cygnus (or Dragon 2 or Starliner for that matter) was launched with no Science payload at all, could it carry more fuel for attitude control / orbit boost? I assume that the propellant tanks get topped off for every launch, but maybe not if they are compromising for up-mass to the space station. If they are full I wonder how much of an engineering challenge it would be to add and connect a reserve tank in the un-pressurized cargo section?
No, tanks are full. Just add larger tanks to Cygnus. Dragon would require a propellant disconnect, which hasn't been with hypergols.
If Cygnus (or Dragon 2 or Starliner for that matter) was launched with no Science payload at all, could it carry more fuel for attitude control / orbit boost? I assume that the propellant tanks get topped off for every launch, but maybe not if they are compromising for up-mass to the space station. If they are full I wonder how much of an engineering challenge it would be to add and connect a reserve tank in the un-pressurized cargo section?
No, tanks are full. Just add larger tanks to Cygnus. Dragon would require a propellant disconnect, which hasn't been with hypergols.
Thanks for the clarification, I wasn't sure if there were any trade-off calculations that were made when manifesting payloads to reduce fuel load in order to increase payload. This is done with military cargo aircraft all the time, but I guess the mass percentage that fuel represents on Dragon or Cygnus makes this not worthwhile, or the amount of fuel on-board already represents a bare minimum for mission execution with little in reserve.
There is a lot of propellant in both crew vehicles for launch aboard that AFAIK won't be used during a normal mission. Or am I mistaken on this? The thrusters in the dragon capsule are places less favorable for station boosts. But on StarLiner they are placed favorable. So AFAIK station reboosts could be done with the crew visiting vehicles.
ISS reboost is planned with Cygnus NG-17. (ISS reboost was a requested capability for CRS-2)
The station has to be rotated so the reboost is done in the right direction. The rear port of Zvezda (the leaking part) is the only location where reboost can be done without changing the orientation of the ISS.
I think both the Nadir port of Node 1 for Cygnus reboosts and the IDA2 at Node 2 forward with crew vehicles are locations that could be used for station reboosts. IDA2 (Crew vehicle, or Dragon XL) are AFAIK in a better location because more modules are aligned in the reboost direction. Node 1 Nadir, is putting more stress on the connections between the sections of the ISS, bit it's closer to ISS center of mass.
Is my thinking correct; that moving a control moment gyro in a direction, the station will start rotating in the opposite direction. By moving the gyro, the station is accelerated in the opposite direction. The ISS keeps rotating in the direction with constant angular velocity. To stop the rotation of the ISS, the control moment gyro has to be moved back to it's original orientation. If this is correct the station can be rotated using a little power and the control moment gyro's.
I'm curious how the reboost using Cygnus NG-17 will be executed.
I'm curious how the reboost using Cygnus NG-17 will be executed.
Along with rotating the ISS, I believe the Cygnus engine can now gimbal, so that it can point to the ISS centre of gravity.