# Tag Info

46

The X-15 had a reaction control system for all three axes using thrusters with hydrogen-peroxide monopropellant. There was an automatic as well as a manual mode. The manual mode used a single three-axis control joystick. There were two completely independent systems. Each system used six RCS thrusters, two for each axis for both rotation directions. See ...

39

The X-15 has a reaction control system. In this image, it's item 2, 13 and 28, labeled 'ballistic control system'. It was operated via a joystick. Detail of two of the thrusters:

36

As someone who has designed a Canopus tracker, it's really very simple. The Sun is generally the easiest thing for a spacecraft to orient to, regardless of orbit or location in the Solar System. So, once you've found the Sun, orient your spacecraft accordingly. You usually have solar panels that you want oriented toward the Sun, radiators oriented away. ...

34

The pendulum fallacy is the belief that rockets would be passively stable with engines at the top, with the rocket "hanging" from them. The error lies in expecting gravity to pull the body of the rocket down while the engines pull it up. In reality, gravity acts on the body of the rocket and the engines equally, exerting no torque (except for ...

31

This answer assumes that the spacecraft is in an orbit which is mostly aligned to the ecliptic plane. A target, whose orbit is also close to the ecliptic plane, can occasionally go in front of the Sun or behind it. In both cases, the star tracker camera should not point towards the Sun, even by accident. It may damage the sensor. Planets orbit the Sun and ...

25

The attitude thrusters and TCMs are mechanically identical, all Aerojet MR-103s. From the Voyager Press Kit: The 16 thrusters on the mission module each deliver 0.89 N (0.2-lb.) thrust. Four are used to execute trajectory correction maneuvers; the others in two redundant six-thruster branches, to stabilize the spacecraft on its three axes. Only one branch ...

23

In the inverted pendulum problem: gravity exerts a vertical force on the pendulum, at the center of gravity the support of the pendulum (like the finger under the pencil) exerts a vertical force on the pendulum, at the bottom of it In a rocket: gravity is the same engines exert a force along the long axis of the rocket, where the engine is (which doesn't ...

14

In 2015-2016, the New Glenn design was expected to use a single BE-4 methane-LOX engine on the second stage (about 2400kN thrust), and a single BE-3 (the same as the suborbital New Shepard's single engine, and likely in the 500-600kN range for the upper stage version) on an optional third stage. There wasn't any need for an engine in between the power of the ...

13

I think they did (page 120): The reference is a bit indirect, but the water storage was right next to the 'exercise ring' (storage lockers):

11

The thruster configuration can be seen better in this image:(cropped from this document ). The attitude control thrusters are not in plane with the direction control thrusters. This Raytheon patent on MKVs states that "attitude control system includes multiple thrusters offset from the center of gravity that provide yaw, pitch and roll control." All four of ...

11

This is not a full answer, but some numbers: What are the ISS moments of inertia around design axes? The total moment of inertia of the station is about $M = 55\cdot 10^6 \rm kg m^2$ How often must the ISS desaturate its control moment gyros? The reaction wheels are desaturated when they reach $13000 \rm ft lbf sec$ which is $L = 17 \rm kJs = 17 \rm kgm^2s^... 10 Without any time markings, it's impossible to tell if the ground track indicates a "hard left" or very gentle maneuvers over a long period of time. The annotated transcript gives us some hints, though: [Pete is descending very slowly as he flies along the north rim of Surveyor Crater, looking for a good spot to land.] [Conrad, from the 1969 ... 10 Does it have three unequal principal moments of inertia... Does the ISS have three distinct principal moments of inertia? The answer is definitely "yes". Any object has a mass matrix,$M$. In three dimensions, this is a$3x3$symmetric matrix. Because$M$is symmetric, such a matrix can be diagonalised, so that$P^{-1} \cdot M \cdot P = \bar{M}\$ is a ...

9

The Shuttle Orbiter's Inertial Measurement Units (IMUs) had four gimbals. The IMU consists of a platform isolated from vehicle rotations by four gimbals. Since the platform does not rotate with the vehicle, its orientation remains fixed, or inertial, in space. The gimbal order from outermost to innermost is outer roll, pitch, inner roll, and ...

9

Gemini had a four-gimbal system as well: The IMU is the usual gimballed stable platform with accelerometers and angular resolvers as in Apollo, except for a key difference that the Gemini IMU had four gimbals rather than the three gimbals of Apollo. This means that it was not subject to the phenomenon of "gimbal lock", and hence the software used to ...

9

As you rightly point out in your question, Canopus star trackers are pretty nifty instruments. I don't think it's really possible to do them justice in a single post, so I'll include a few summarizing points here and will include links to other articles, etc. for more information. 1. How do they work? NASA Technical Report 32-1559 does an excellent job of ...

9

A naive bang-bang approach can consume excessive amounts of propellant when the vehicle needs to achieve large changes in attitude. The rotation rate can get excessively large at the switchover point. The solution is simple: Don't do that. There's typically no reason to make (for example) a 180° rotation in the minimum amount of time required. Many vehicles ...

8

I'm interpreting this question as "Did adjustments have to be made to the shuttle Digital Autopilot (DAP) while it was controlling the mated stack (shuttle + ISS) - i.e. was a maneuver tried, the results of the trial evaluated, and the DAP settings changed based on the results of the trial during the same shuttle mission?" If that interpretation is correct, ...

7

I don't think it's happened in a long time, but in the early stages of assembly, the ISS sometimes flew in a "XPH" attitude when the beta angle* was between 10 and 75 degrees. The only public info I could find on this is from a rather annoying flash animation NASA page; it shows some animations of the orbits, here are two frames from the XPH example showing ...

6

The conversion of the attitude data as it appeared (undocumented) from Lightstreamer to roll, pitch, and yaw was the biggest pile of guesses and assumptions atop assumptions I made back when Matt and I were coding this. It is almost certainly wrong if it is varying from the ISS Live! website. We've been working on a complete rewrite of the code and it'd be ...

6

Per Elon via twitter, magnetic torquers. Magnetic torque rods for desaturation of momentum wheels.

6

Voyager's thrusters are in 3 groups: 2 branches of 6 attitude control thrusters (which provide rotation around the major axes). The 2 branches provide redundancy 1 set of 4 trajectory correction maneuver thrusters which were designed to provide translation. By firing them individually instead of in pairs, they can provide pitch and yaw (but not roll). This ...

6

And what is the big black rectangular "bay window"? That is one of Hubble's radial instrument bays. It currently holds the Wide Field Camera 3. This DOUG rendering shows the camera "popped" out of the bay. why do the two lower ones point nearly in the same direction? As this answer says, the three orifices below the "bay window" are the openings for ...

5

In this figure, ζ is the input axis, η is the output axis, and the spin axis is obvious. If the vehicle is rotated around the axis ζ (the input axis) with an angular velocity ωζ, the frame will rotate around the axis η (the output axis) to an angle β. The dependence of this angle on ωζ is given by the equation β = ωζH/c, where H is the moment of momentum of ...

5

By integrating inertial measurements, initialized from the final star tracking about 20 or 30 minutes earlier. Also, from Spaceflight 101: With the separation of the Cruise Stage seven minutes before re-entry, the InSight spacecraft solely relies on its MIMU for attitude propagation, rate measurement and the deceleration trigger for the critical parachute ...

5

When you're trying to rotate something, there are two cases: 1) The torque you're applying is large compared to the angular momentum the body has, i.e. when the body isn't rotating. Then it starts to rotate in the direction of the torque you're applying. This is the more intuitive case. 2) The torque you're applying is small compared to the angular ...

5

A hemispherical resonator is an example of a mechanical gyroscope that has no bearing parts and for practical purposes no moving parts either. See the Wiki page here. I actually find the description of the principal of operation there a little hard to follow so I've just taken the black box principle, that the vibration patterns in the surface respond to ...

5

It boils down to: how much spacecraft resource is required by the attitude control method you propose using? And sometimes the mission's pointing requirements play a significant role. Thrusters use propellant. Reaction wheels (and momentum wheels) use electric power. Spin stabilization uses neither, as long as you don't need to repoint the spacecraft — but ...

Only top voted, non community-wiki answers of a minimum length are eligible