Hot answers tagged

53

You are misreading the accident report. By 14:00:02, the vehicle had already begun to lose structural integrity, it had already begin to lose thermal integrity, and it had completely lost control authority. I'm going to digress a bit to distinguish between faults, errors, and failures. As a simple example, consider a bit in computer memory that permanently ...


32

The RCS wasn't depleted. The RCS firing was a symptom of a main issue, and it happened very late in the timeline, at 13:59:29. The RCS fired after the spacecraft's left yaw went beyond the capacity of the aerodynamic controls to compensate for it, Loss Of Control happened at 13:59:37, just 8 seconds later. The Loss of Control was due to a complete hydraulic ...


29

For Shuttle EVA, the Space Shuttle Flight Rules show that the safe distance for a suited crewmember was 27 feet for the main jets, 3 feet for the vernier jets, and 3 feet for the APU exhaust. It's rule A-15-22 in the document. This rule is probably a simplified version of what would actually be managed to; I remember seeing "Keep Out Zones" (KOZ) ...


27

There are several reasons not to do this: Artificial gravity in such a small space is not very pleasant. You'll get a noticeable difference in gravity in different places, which makes it difficult to move around without banging into the walls. You also get coriolis forces (thrown objects don't move in a straight line) which makes moving around non-...


22

The columbium jet nozzles themselves can take the heat, but "penetrations" of the spacecraft heat shield are a definite potential failure point, including penetrations for the Reaction Control System (RCS) jets. The design to preclude hot gas intrusion while preventing damage to the surrounding Thermal Protection System can be quite complex. The forward ...


16

The highest rotational rate ever achieved by a shuttle in orbit was only 3 degrees/second (approximate). This was inadvertently caused when Mission Control uplinked a bad state vector during crew sleep* and caused the vehicle to go out of control. This rotation rate was not nearly enough to induce artifical gravity. *incident is described on pages 2-4 ...


14

A space ship may need some protection against the heat of its own RCS thrusters. The Apollo Lunar Module was covered with multiple layers of thermal insulation foil. Close to the RCS thrusters the top layers were made from from nickel and the high temperature alloy inconel. The thermal blanket consists of multiple-layered (at least 25 layers) of ...


12

The Orbit Attitude and Maneuvering System (OAMS) was for orbit and was jettisoned before the retro burn, leaving the RCS for reentry. The com­plete OAMS had 16 small engines, which burned hypergolic propellants fed under pressure from one fuel (monomethylhydrazine) and one oxidizer (nitrogen tetroxide) tank. All engines were mounted in fixed positions and ...


11

Actuator saturation is a control systems terminology. It means that the required (requested) control input exceeds the physical limitations of the actuators. For example once a valve is fully open you cannot ask for more fluid since it is fully open. But the cooling system might ask for more numerically from the valve due to some excessive heat (a ...


11

The CM entered the atmosphere blunt-end first, which became the hottest part during re-entry (see picture below left). So you can't place RCS thrusters on that part of the CM, as they would melt; you can only place them on the sides of the cone, where it stays cooler. Thus, the CM had no aft-facing ($-X$) RCS thrusters. Note that the side of the CM toward ...


10

As Organic Marble notes, some single-engine stages do use RCS for roll control since the requirements for roll on ascent are less demanding than pitch and yaw. The Falcon 9 first stage also uses RCS to control its attitude during the early phases of its reentry trajectory, where the grid fins are less effective. It's possible in principle to use RCS for ...


9

The concept and formula are correct for a coherent system of units. You have chosen to use US customary units and these are not a coherent system, i.e. in the situation in the OP one is bound to run into trouble. Looking on the bright side, your sense of what range the right answer could be in definitely helped you out here! There are several ways of looking ...


9

Some resources (Wikipedia, Astronautix) give 312 seconds for the R-4D, but I think that's for the large-nozzle modern version. Marquardt's "Apollo SM-LM RCS Engine Development Program Summary Report" gives the nominal specific impulse as 280 seconds, and gives figures for flown engines on Lunar Orbiter I-V as 276.1 to 279.5 seconds. The Lunar Orbiters, the ...


8

TL;DR: It is used unto the very end, so somewhat near $0\ \mathrm{km}$. The RCS is used in re-entry right from the Entry Interface ($125\ \mathrm{km}$ from the Martian surface, $5,900\ \mathrm{ms^{-1}}$), at which it is pressurized and subsequently used for controlling roll, pitch, and yaw as directed by the entry guidance unit. It shares the same ...


7

Monopropellants are less efficient than most serious bipropellant rockets, including hypergolics (though hypergolics are themselves less efficient than some other propellant combos). In impulse per propellant mass (specific impulse) and often also impulse per propellant volume (impulse density), monopropellants aren't great. For a reusable craft, this may ...


6

Not likely. For early manned missions, rendezvous wasn't a requirement, so thrusters provided only for rotation, not for translation. According to this reference: In each of the two [redundant] sections of 8 [thrusters] there were 2 thrusters each for pitch and yaw and 4 for roll. Depending on how the thrusters were offset from the craft's center of ...


5

Puffin's answer is correct; this is just a supplemental that was a bit too involved for a comment. A physical interpretation of specific impulse measured in seconds is "the length of time for which one mass unit of propellant can provide the force needed to balance the mass against Earth gravity". Therefore 1 lbm of propellant with 73 sec Isp ...


5

Service Module RCS: 8 max There are 16 engines total, arranged in four groups of four ("quads"). You can fire 8 of the engines by placing the Direct RCS switch to ON, and then turning either rotational hand controller to its extremes in all 3 axes (pitch, yaw, roll). Each axis of a rotational controller has limit switches that are activated when the ...


5

An "RCS opening" is a rocket nozzle, which has to withstand massive heat loading from engine burns. Massive enough that the nozzle will also withstand the heat load on reentry. You just have to make sure there's no gap between the nozzle and the heat shield around the nozzle.


5

Your suspicion that it can be done with 4 is correct, and the method you suggest will work. More formally, to prove that a set of thrusters allows arbitrary torque is equivalent to showing that you can produce torque in each direction about the 3 orthogonal axes shown. The ones drawn allow +blue and -blue (the two equatorial thrusters), +green (the one at ...


5

Although perhaps larger than what would normally be considered RCS, the Ares-1X solid rocket booster did use jets to control its roll attitude in first stage (its only stage, for this test). Pitch and yaw were controlled by gimbaling the nozzle. Reference: https://en.wikipedia.org/wiki/Ares_I-X#Roll_control_system


5

sub-partial answer... Shuttle used a table lookup method to determine which jets to fire for a desired maneuver. If the full tables are available online, I am not aware of it, but there were some examples in training material. For background on the shuttle RCS and its operations please review the following answers first: https://space.stackexchange.com/a/...


4

It turns out I made a dumb math error (a transposition, specifically), related to this math.stackexchange question. In short, I was computing $\mathbf{\lambda} = \mathbf{\hat{A}}^{-1}\mathbf{\hat{c}}$ instead of $\mathbf{\lambda}^\textrm{T} = \mathbf{\hat{c}}^\textrm{T}\mathbf{\hat{A}}^{-1}$. It still produced what appeared to be valid answers in many cases ...


4

I think the CSM/LM Operational Data Book Volume III: Mass Properties has what you're looking for. Because mass and mass distribution vary as consumables are consumed, I don't think it provides a single convenient inertia tensor (although I wouldn't recognize one if it walked up to me on the street and said "hi, I'm a 3x3 inertia tensor"), but: data are ...


4

One can "start" or "execute" the "burn" or the "maneuver". Examples are found in the Shuttle Crew Operations Manual on page 7.2-3 To perform an automatic maneuver, the crew first enters the required data on the UNIV PTG display for the desired maneuver. To start the maneuver at a set time, that time is also entered on the UNIV PTG display. After ...


4

Assuming this simulation is correct, and I have no reason to doubt that it is, there is in fact true 6 degrees of freedom of movement possible. I do recall that at least one of the axis has less control, but I can't find the news report that states how the manual control felt according to the astronauts...


4

RD-107 seems to have been used in the R7 missile. It says in the article for the missile that 1st stage: 4x jettisonable four-chamber RD-107 booster engines each with 2x vernier rocket engines plus 1x four-chamber RD-108 core engine with 4x vernier rocket engines. So the RD 107 stage was used in quadruplets. So vernier engines existed on diametrically ...


3

I'm going to interpret your question as being: "What factors drive the choice between bipropellant and monopropellant thruster systems for spacecraft maneuvering systems?" If that's wrong, advise in a comment, and I'll delete this. This answer is a summary of the paper Performance Evaluation of Spacecraft Propulsion Systems in Relation to Mission Impulse ...


3

I found transverse acceleration for the Space Shuttle Orbiter on page 1009 of the Shuttle Crew Operations Manual (December 15, 2008). I don't know how to reproduce the table here. But it depends on weight, of course. Also axis and direction. At 180,000 pounds (lightest weight in the table), max of 0.61 ft/s^2 in +X (noseward), apparently 0.32 in -X, 0.22 in +...


2

Am I correct in saying that all four engines of each of the four quads could be fired independently of one another, i.e. in any combination? Note that I am not asking whether the control software did it this way, but whether the physical RCS propulsion subsystem was capable of firing all four engines per quad, and all four quads (i.e. a total of 16 engines) ...


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