# Tag Info

28

This is exactly how it works and how the orientation of many satellites is controlled. For example, the Hubble telescope has 4 fidget spinners installed, pointing in different directions - although they are commonly referred to as "reaction wheels". Unfortunately a typical fidget spinner is a bit too light to be really useful: We have to compare ...

18

TL;DR Star trackers are by far the most precise. Sun sensors are used for coarse knowledge and IMUs only for estimating the attitude during a maneuver. Details Attitude determination typically relies on several sensors. Most (all?) spacecraft have at least two modes: coarse and fine attitude determination. The first is to have a general idea of your attitude ...

16

Most spin-stabilized rockets are solid-fueled, so slosh-free. Solid fueled stages also tend to have heavier structure than liquid-fueled ones, because the propellant container needs to contain combustion pressure, so they are less bendy than a liquid stage of similar volume would be. The proportions of spin-stabilized solid upper stages tend to be fairly ...

12

Some solid rocket motors provide thrust vector control by injecting fluid into ports around the nozzle. In this system, neither the nozzle nor engine is gimbaled. Vehicles that utilize(d) this system include later Titans and the PSLV. My answer to this question includes a description of the Titan system with schematics: What was the purpose of the small red ...

12

Neither fins nor Dracos, a dedicated cold-gas system. Source: https://space.stackexchange.com/a/23654 Confirmed by the Falcon 9 User's Guide (April 2020 version) In addition, the second stage contains a cold nitrogen gas (GN2) attitude control system (ACS) for pointing and roll control. (emphasis mine)

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 ...

8

The sample return capsule has no active attitude control system. It is ejected from the main spacecraft with a 20 rpm spin. Since the reentry capsule is flown by totally passive aerodynamic stability, the flight characteristics are to be carefully investigated both statically and dynamically, throughout the entire reentry flight and descending flight ...

6

GPS? Yes but basically you have to have several (at least three) antennas that are widely spaced apart. You can either have separate GPS systems at each antenna and use simple trigonometry to calculate your attitude, or feed the the signals from all antennas to a fancy receiver that solves the whole problem at once. Current status of the use of GPS mutli-...

5

The most accurate attitude determination depends very much on the needs of the vehicle. It is important to remember that perfection is the enemy of good enough. Different spacecraft have different requirements for what "good enough" is. Going beyond "good enough" is not very smart. But what if the "good enough" requirement is ...

5

Are bicomplex numbers including tessarines ever used in spaceflight (as an alternative to quaternions)? Without the parenthetical remark, the answer is "I don't know". But with that parenthetical expression, the answer is all-caps "NO". Unit quaternions are used in space exploration precisely because they map nicely to rotations in three ...

4

In short, its measurement of attitude compared to external references. I couldn't say for "pure" solar sailing missions - where the aim of the mission is to demonstrate a large sail, however: Context Some geostationary communications satellite missions employ solar sailing as an attitude control technique exactly as the OP describes with a ...

4

The order in which the rotations is performed always important in an Euler rotation sequence. You can show this to yourself by picking up a book and applying a roll / pitch sequence versus a pitch / roll sequence. This is very unlike translation, where first going 1 km north and then 1 km east brings you to the same point as does first going 1 km east and ...

4

With modern computers and software models of spacecraft, there is no reason not to take the "shortest path" approach when adjusting a spacecraft's attitude outside of certain edge scenarios. This is because, for a computer, adjusting all three axis simultaneously and handling the potentially complex interplay/second order effects resulting from ...

4

This paper is a sizing exercise, made before the thrusters in question had been flown on any spacecraft. The moment of inertia can be backed out from the numbers in the article. Given the bang-bang control scheme used in the article, the relation between angular acceleration $\dot \omega$, firing time $t$, and angular change $\theta$ is \frac12\dot\omega\...

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...

3

I believe I have worked out my own question using http://www.dept.aoe.vt.edu/~cdhall/courses/aoe4140/attde.pdf This uses the TRIAD algorithim in order to determine a rotation matrix between the body and inertial frames by knowing two vectors in both frames. Usefully, it also weights one as being more accurate than the other which in this case is likely to be ...

3

It's probably the system used by the Gaia mission, which uses the astrometric telescope payload as its most precise sensor. "The challenges for the AOCS design are to provide attitude control within a restricted pointing domain, due to thermal constraints, and to provide a fine pointing mode with relative pointing error (RPE) of a few milli-arcseconds (...

3

I don't know of any source that would give a comprehensive survey to this kind of question, so answers are probably going to come from people who remember specific examples. If they remember which ones to look up and verify. I've seen some but can't remember which ones, so I haven't said anything. But I just read about the Japanese Mu-3 family of rockets, ...

3

Note that Explorer 1's spin stabilization worked fine for getting it into orbit. Dissipation during the few minutes of thrust was not enough to cause trouble.

3

This is how it worked for the Space Shuttle, it was fairly autonomous. To perform insertion, orbit, and deorbit maneuvers, there must be accurate data for the orbiter's location and velocity with respect to the Earth for use by guidance and control. This is the task of the shuttle navigation software. The navigation software maintains an accurate estimate ...

3

This answer is somewhat speculative and relies upon a generous interpretation of what "minimizes accelerations" means. I obtained a three-view drawing of the Voyager from a link in this answer What does it mean when the Voyagers "switch thrusters"? I've cropped and annotated a portion of the drawing dealing with the pitch thrusters. ...

2

A dynamically unstable spinner can be operated with Active Nutation Damping. This "simply" means using a control loop to conduct small manoeuvres to reduce precession. The direction of the thrust is in the body spin-axis and is at a finite radius from the spin vector (the further out the more effect per pulse). Obviously it needs quite precise ...

2

I know this question is old, but I randomly discovered a solution requiring only three thrusters on one thruster block that works if we don't mind introducing small transverse velocities. We need a thruster block that has is three thrusters at ninety degrees from each other all tangental to the satellite's surface, or in other words, a typical RCS quad with ...

2

I do not know how exactly the attitude is presented to the crew, my experience is tied only to the unmanned spacecrafts, though I would imagine there is no unique preferred solution and it depends on the particular task at hand. I will try to provide some possibilities at least, but first a slight correction. You mention the rotation matrices and quaternions ...

2

It's possible to use reaction wheels to arbitrarily alter one's attitude, but a major limitation with reaction wheels is that if an object has rotational momentum and one wants it to maintain a constant attitude, the reaction wheel will have to spin forever unless or until one gives up on holding a constant attitude or one can transfer rotational momentum ...

1

Each thruster will have a thrust vector. That can be resolved into torque and translation depending on the CM. If you have six thrusters you should be able to get all six degrees of freedom. If you want one pure degree of freedom you have to solve a set of simultaneous equations, which is not hard. If there is a degeneracy in the system you may not be ...

1

If you consider the grid fins at a small angle of attack, am I right that drag will act in the direction of the flattened axis (thickness of the grid of fins) and that lift will act perpendicular to it? For any body in a flow, you can draw a single net aerodynamic force vector. Conventionally, the component of this vector inline with the vehicles ...

1

Tessarines are quite like numbers, and quaternions are more like 3D vectors plus one more special dimension. It is natural that vectors are useful in kinematics. On the other hand, split-complex numbers are related to Minkowski space, so if space farers ever need extensive calculations in special relativity, split numbers may be of use.

1

Seems like usually 100 newtons - 440+ newtons of thrust. This depends on many different factors, though, including the gas being used, the pressure its being fired at, and the size of the nozzle/the mass of whats being fired. This wikipedia page has information about the gemini spacecrafts' thrusters. https://en.wikipedia.org/wiki/Reaction_control_system ...

1

"Novel" here means in respect to other planetary missions, and also the thruster fuel: the previous missions to the outer planets (Pioneer) were spin-stabilized, and previous missions to the inner planets used cold-gas thrusters. A quote from later in the same paper in your question: The Voyager spacecraft incorporate several improvements to ...

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