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Questions tagged [attitude]

Questions on ascertaining, predicting, and controlling spatial orientation and rotation of spacecraft, and on forces that affect spatial orientation.

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How can gimbal lock occur with three perpendicular reaction wheels?

I understand how gimbal lock is a serious risk in case of CNG where the axis of rotation change in operation, and as they become coplanar you lose degrees of freedom, the respective axis duplicating ...
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Are robot arms ever used for attitude control in space?

Motion of a robotic arm mounted on a spacecraft presents an interesting challenge from a control perspective. A robot arm, such as Canadarm (space shuttle) and Canadarm2 (ISS), has significant mass ...
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Attitude control systems with only reaction wheels

With reaction wheels it is common to use actuators such as Thrusters and magnetorquers, to account for the saturation of the reaction wheels due to secular/non-cyclic disturbances. However, these ...
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1answer
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Verify solar radiation torques on a satellite

I'm creating a design support system for Attitude control design of a spacecraft. For the attitude simulator, I have made a function to compute the solar radiation torque acting on the satellite which ...
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What is the Lux value of the Sun and Earth in Low Earth Orbit (altitude=400 km)?

I'm the Attitude Control System team lead on a cube satellite project, and we're trying to use cheap lux sensors to determine the body sun vector (vector adding the lux from each sensor). I want to ...
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Falcon fairing half - between separation and parachutes deployment

How does Falcon fairing half behaves in atmosphere before parachutes deployment? What is its free fall attitude in atmosphere? Is the fairing's attitude stable (with some wobbling, but without ...
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2answers
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What sensors or combination of sensors do rockets use during takeoff for their orientation?

I know that after using up rockets and before reaching final orbit, satellites use Earth, Sun, Star trackers to find the absolute position depending on the application and orbit. After that, they use ...
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What attitude have past and modern manned spacecraft maintain(ed) relative to Earth?

I hope this question is not too broad. It is inspired by another question. We know that ISS keeps its nadir pointing to Earth's surface. What about other manned spacecraft? Do/did they have ...
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Have any vehicles used asymmetrically variable thrust for active stabilisation? [duplicate]

Have there been any tests or attempts at developing a propulsion system that uses variable thrust for attitude control (particularly during launch)? Conventional systems often use fully gimballed ...
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1answer
130 views

Attitude requirements for inter-satellite laser communication

Previous questions have address the beam divergence angles and the expected signal attenuation for laser communication between spacecraft. However, I was wondering what is a typical receiver aperture ...
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What is the difference between dual-spin spacecraft and hybrid(attitude control) spacecraft?

The definition from this source is "Two classes of spacecraft bring together the advantages of having momentum bias and yet provide a non-spinning base for accommodation of payload elements and ...
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What is a non-propulsive vent?

I just hear the term "non-propulsive vent". Is it a thing, a vent that does not cause propulsion? Or is it an event, where a vent of some unwanted gas has occurred which did not result in a ...
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Spacecraft Horizon Sensors for Lunar orbit

Recall that "traditional" horizon sensors for Earth missions utilize the IR wavelength regime since this can reveal a good contrast between the cold space and the warm Earth-limb edge. If we were to ...
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Atomic Inertial Sensor

In relation to the question I was looking for the perfect sensor that would help me achieve perfect non rotating spacecraft. My search made me look for exotic phenomenon that can be utilized for such ...
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2answers
162 views

Using what technology one can keep a spacecraft truly non rotating

Inspired by the question I thought maybe a photon thruster can be used for precisely giving thrust to maintain spacecraft attitude. But soon I realized that for high precision attitude control, one ...
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Attitude and orbit thrusters catalog

Typically, when trying to adjust simulation parameters (of orbit control, attitude control...) to real world values in order to validate algorithms with comparisons with past and current mission ...
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1answer
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Angled thrusters on the Soyuz 2.1a?

I saw a satellite launch recently (launch link) which used the Soyuz 2.1a rocket. Shortly after the launch I observed 4 symmetrical thrusters at an angle to the main thrust line. Is this for ...
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Can you turn in space without propulsion?

Say an astronaut is floating perfectly still inside their spaceship. Can they rotate themselves by stretching out their arms and twisting one way, then pulling in their arms to their sides and ...
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Finding reference quaternion of a satellite in orbit

How can i find the reference quaternion of a satellite after it has detumbled? I need the quaternion to be able to successfully actuate my payload, which in this case will be a hyperspectral imaging ...
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1answer
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Change a Spacecraft's attitude from 3 - axis stabilised to spin stabilised?

I am essentially trying to "spin up" a s/c, so it spins about 1 axis at a known spin - rate. I then need to figure out how much time it will take to do that, and how much force required (which I ...
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2answers
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Did Tiangong-1 turn the engines on?

The following graph shows the Tiangong-1 radius vector at the perigee, semi-major axis and apogee (scaled to 6371 km just to show an approximate altitude) and its orbit eccentricity: I used the SGP4 ...
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Initial attitude determination after deployment

Suppose that I am launching a cubesat into space. Let the cubesat be launched from the P-POD deployer. Since the satellite will have a huge velocity, hence the detumbling mode will be operating. As ...
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1answer
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Inexplicable Offset in Satellite Laser Ranging (SLR) observations

I am struggling with the implementation of a Satellite Laser Ranging (SLR) validation tool. The situation is as follows: I am provided with a framework which gives me the position of a SLR ...
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How does Voyager 1 keep track of its orientation?

With the Voyager 1 attitude correction all over the news (related: How do Voyager 1's Trajectory Control Thrusters differ from its Attitude Control Thrusters?), I wonder with what instrument such ...
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How do Voyager 1's Trajectory Control Thrusters differ from its Attitude Control Thrusters?

There are several popular news items about the recent test of Voyager 1's Trajectory Control Thrusters to see if they can be used for attitude control to facilitate communication with Earth. The ...
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1answer
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In what circumstance would it be useful for a satellite’s angular velocity to differ from its reference frame’s angular velocity?

Casually reading “orbital mechanics for engineering students” on rigid body attitude dynamics, i see the following passage: $$M_{net}=\dot{H}_{rel} + \Omega\times H$$ Keep in mind that, whereas $\...
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Did any rockets use differential throttling instead of gimbal?

It seems the standard approach to control of rockets during launch is either vernier thrusters, or gimbals on the main engines. Sure that works, and is quite efficient, but I wonder about a simpler ...
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Will Mayak's large solar reflector produce a stable attitude, or is it likely to start tumbling or rotating?

In this question I've asked about the possible reflection of UHF radio signals from the recently launched Mayak cubesat once it's large metallized polymer solar reflector is deployed. However it will ...
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3answers
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Xenon vs Hydrazine, “Should I Stay or Should I go?” Dawn mission decisions

edit 2: There seems to have been some announcement/extension by NASA (20-Oct-2017), possibly this will shed more light on the issues in this question. edit 1: Several months have passed since this ...
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2answers
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Does the Hubble telescope use a “simple” PID-controller for its pointing control system?

I am wondering whether the Hubble Space Telescope uses a "simple" PID controller like this: Or is it using another type of control system that may be much more complex?
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1answer
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What determines if a star tracker blends two stars that are close to each other?

If two stars are very close to each other, a star tracker could identify the pair as a single star, with a magnitude and position different from both stars. This obviously impairs the software's ...
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216 views

Controller to reaction wheel interface

A typical controller generally gives control torques which should be applied about the axis of a satellite. How exactly is this torque applied using a reaction wheel? For example if control torques ...
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134 views

What are the main properties of the CMGs on the ISS

How large (mass) are the CMGs on the ISS? What is the minimum torque they apply? What is the maximum torque they apply?
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What are the disturbing torques on the ISS?

What are the orders of magnitude of disturbing torques on the ISS itself, preferably split into the following categories, but any numbers (with source) will be useful: Gravity gradient Magnetic Solar ...
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How well and how rapidly can the ISS attitude control system detect periods of astronaut activity?

The question Why doesn't ISS start to spin if people walk inside? is a good one partly because it has attracted several good, informative answers. One of them is particularly intriguing because it ...
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Why did New Horizons have to be spin-balanced to grams-level precision? (With quarters!)

This story about receiving a roll of Space-Themed Florida State commemorative quarters from the Governor of Florida mentions that the New Horizons spacecraft had to be "spin-balanced" to grams-level ...
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1answer
572 views

How do rate gyros measure yaw, roll and pitch rates?

I need some help in understanding how rate gyros are used for measuring rotation rates about the yaw, roll, and pitch directions. Suppose a gyro is used for measuring roll rate. How should the spin ...
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What are the sizes and locations of Progress's thrusters?

Supposedly the Progress modules used for ISS reboost, attitude control, and debris avoidance have two large engines and some number of steering jets. I know Zarya has 24 large and 12 small in ...
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214 views

Is this an ECI frame?

I am reading a document on satellite attitude control and the Kalman Filter and it mentions that the satellite is tumbling through free space in a reference frame that has the Sun vector of constant ...
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Simulation software for AOCS/GNC?

I would like to know what are the simulation software tools available as of today (free or commercial) to perform some attitude and orbit control (AOC) or guidance and navigation control analysis, I ...
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1k views

How does a single SRB control attitude?

The Ares I-X was a test flight from the Constellation program for crewed Ares I-launched Orion capsules. If liquid fueled rocket motors can gimbal, how do solid rocket motor-propelled spacecraft ...
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2answers
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At what RPM does a desaturated reaction wheel run?

A plenty has been written and said about reaction wheels on this site, but there's still one thing I'm curious about: what's the "nominal/rest" speed of a reaction wheel? Say, we've just finished the ...
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Why are the ISS attitude values shown on these two web sites so different?

Here are screen captures from two sites that seem to be showing approximately live - or at least changing - telemetry from the ISS. They both say the spacecraft attitude is shown in degrees. Looking ...
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Spice PCK planet orientation model

I'm looking at this SPICE kernel, which contains orientation data for planets and other bodies. Model description and examples in "Orientation models" section look pretty simple. But actual numbers ...
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1answer
115 views

How different is communication between passive and active ADCS?

How different is the communication to ground stations between passive and active ADCS? Also, is there any data or insight into probabilities of ground station contact with passive?
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226 views

Could the ISS stop rotating wrt the stars for a few days, then start again?

Suppose for some reason it was particularly advantageous to stop the ISS from rotating once per orbit, so that it maintained a constant attitude with respect to the stars (or the Sun) instead of with ...
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1answer
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What are quaternions and how are they used to represent spacecraft dynamics?

The title says it all. Quaternions are widely used to represent the orientation of a spacecraft. Why is that, and how do quaternions compare to other alternatives?
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What does “Q frame” means in terms of satellite coordinates?

I'm looking at some old satellite documentation which mentions the use of a "Q frame" coordinate system to keep track of the satellite attitude. What does this "Q frame" generally mean in the field of ...
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How are the Voyagers' thrusters configured in a novel way to minimize accelerations along Earth-spacecraft axis?

I've just read in Eshleman et al 1977 Radio Science Investigations with Voyager that the voyagers have: a novel attitude-control thruster configuration that minimizes accelerations along the Earth-...
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Do ring laser gyros age with laser and dithering disabled?

Laser fading seems to be a known issue with ring laser gyros. With their STEREO-B probe, NASA experienced a different, "unexpected" failure mode, giving false readings. The Honeywell MIMU's were well ...