12
Your first guess was correct.
But it's also possible that instead of preloading the rocket's attitude profile, they would preload the engine nozzle actuator commands required to follow that path.
This wouldn't work, because there are a number of factors that cause trajectory deviation that can't be predicted. For example, engines can slightly over- or ...
8
If the upper stage is fired promptly after first-stage shutdown, it's possible that no ullage is needed at all. The thrust from the first stage engines settles the upper stage propellants. Any separation impulse between the stages tends to keep them settled, and there isn't enough time for any of the ullage gas to drift to the engine inlets before the upper ...
5
A cubesat without a propulsion system deployed from the second stage of the rocket using weak mechanical forces only just follows the trajectory of the second stage. Differences between the trajectories of the deployed cubesats and the second stage are very small.
So the cubesat owners may use the latest trajectory information from the launcher as initial ...
4
Ullage for the Apollo command/service module and the lunar module was performed by those reaction control system engines which pointed in the same direction (+X) as the main engine. These engines are essentially digital in nature; they are either off or on. Some control modes allowed the RCS engines to be pulsed for finer control. However, ullage burns ...
4
You're correct that terminal velocity varies.
For a given vehicle in a given attitude relative to the airstream (i.e. a particular angle of attack), though, it varies only with the air density and therefore primarily by altitude. The $C_D$ varies with airspeed, but it doesn't change very much over the slow subsonic regime of low-altitude terminal velocity, ...
4
According to a simulation at FlightClub.io, aerodynamic pressure for the first stage reentry peaks at about 112 kPa.
4
You don't say how old the document is, but I suspect it's old, even for shuttle.
In the early days, shuttle missions executed an OMS-1 burn to raise the apogee, followed by an OMS-2 burn to circularize the orbit by raising the perigee.
I suspect your document refers to OMS-1.
To answer the part about burn duration, on STS-1 OMS-1 was 86.1 seconds. You can ...
3
Could you make a nuclear thermal rocket using water as a reaction mass? Sure! People have looked at that, as it would be nice to be able to refuel rockets in space from things you find (see Nuclear thermal rockets using indigenous extraterrestrial propellants)
Could you launch from Earth with such a rocket?
Well, maybe.
Would it be worth it?
Maybe not.
Lets ...
3
No doubt many SpaceX employees have dabbled with the Kerbal Space program including Elon, but I very much doubt that it is used for any serious calculations at SpaceX. I’m confident that they have a suit of in house simulation programs available for all astronautical engineering and celestial mechanics type questions for anything more than a back of an ...
3
In my experience, there isn't currently a good solution for this, especially for amateurs, hobbyists, or small commercial operators. These groups often fly small satellites on rideshare missions. For smallsat rideshare, there are a so many uncertainties that removing tracking uncertainty is really important
Uncertainties
Is my satellite dead-on-arrival (DOA)...
3
The launch provider provides the state vectors, based on the deployment force, angle, and the state vector of the rocket stage when the cubesat was deployed. The exact format may vary, it could be a TLE or a state vector or something like that, in any case it will be something both the provider and the customer will agree on well in advance.
2
This is not directly related, but here's a graph from measurements of Apollo.
From NASA tech report 19690029435
The report includes this graph of dynamic pressure as the Apollo capsule returned to Earth. (One pascal = 0.0208854 lb/ft^2 ) These values roughly 29 kPa (peak).
2
For shuttle, the ground uplinked a state vector about two hours before the deorbit burn.
See the Deorbit Prep Checklist, page 1-13. Action is listed as SV UPLINK.
The vector was updated during entry by data derived from its navigation systems.
For entry, the Orbiter additionally used traditional airplane type sensors: air data probes, TACAN, MSBLS, and ...
2
There is nothing official from SpaceX so any algorithm will be based on assumptions. Unlike your question SpaceX will be very interested indeed in exactly where their rocket lands and they will also have to work in 3 dimensions.
A simplified and approximate algorithm should be possible to build “relatively” easily. I would assume each phase of the landing ...
1
Yes, it is only done on engine startup. Remember, ullage is done so that liquid propellant is fed to the engines, instead of gas bubbles. When a tank is allowed to sit in microgravity for a significant amount of time, there is a risk of some of the gas bubbles in a partially-empty tank migrating to the tank's outlet at the bottom. An ullage burn at the ...
1
According to simulations by Declan Murphy, the creator and developer of Flight Club, the profile is as follows:
Light center engine at 80% thrust.
~3.3s later, light additional two engines at 80% thrust.
~15.2s later, shut down additional two engines.
~1.5s later, shut down center engine.
[Sample values from Starlink 1.0 L22 mission.]
1
To my knowledge, this has never happened from a flat surface on land, and has not happened at all with no supporting infrastructure (i.e. there's never been an orbital launch vehicle that you can just set down somewhere and then fly into orbit). There have, however, been orbital launch vehicles which have launched from submarines in the open ocean.
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