Hot answers tagged

33

In 2015, the last original Voyager engineer still on the project, retired. NASA specified that his replacement would have to know FORTRAN. The software was updated regularly after launch: The last true software overhaul was in 1990, after the 1989 Neptune encounter and at the beginning of the interstellar mission. "The flight software was basically ...


13

The Voyager spacecraft are not reprogrammed anymore, so the language in which they are programmed is largely irrelevant. The uplink is only 16 bits/second, just enough to send (simple) commands. How these commands are generated is irrelevant to the spacecraft. Any language that can generate a sequence of bits theoretically suffices. This pdf document ...


12

With the exception of model rockets made of paper, wood, or breakable plastic, that are passively stabilized, that have low thrust and low delta V, and that do not have guidance software, launch vehicles fall under ITAR regulations. The regulations are now much more relaxed once the launch vehicle has achieved its goal and placed its payload into orbit. ...


11

Full disclaimer: I'm the author and main developer of poliastro. The most important step before doing anything is somehow retrieving the positions and velocities of the planets of the Solar System. Astropy, one of the core dependencies of poliastro, ships medium-precision approximate models described in Simon et al "Numerical expressions for precession ...


10

I didn't work on Voyager, but can tell you that deep-space missions tend to retain the original ground hardware, software, language, and build environment, both for continuity/safety as well as budget reasons. There may be little or no funding to continue the mission; it may even fall to outright volunteers. It's amazing and sad to me how much we depend on ...


9

TL; DR: Trajectory optimization for continuous thrust is difficult and this field is very active in research. Edit: Concerning the rotation of your spacecraft, you'll want to plot the in-plane and out-of-plane thrusting angles (with respect to the RNC frame of the spacecraft). That will give you an idea of how much the engines needs to gimbal by before ...


9

First: the main problem with your technique of subtracting the two positions is that it does not account for light-time travel. In the case of the Moon observation that you set up in your code, the error is only about 38 km, which might be well within your tolerances. The way to ask for a relative position that is properly light-time backdated is through the ...


6

This is a problem that has plagued groups of people very knowledgeable about orbital dynamics but who learned using different textbooks: there are two different definitions of "flight path angle"!! In addition to $\gamma$, the angle between the tangential direction and the velocity vector, there is $\beta$, the angle between the radial direction and the ...


6

I would highly recommend NASA Goddard's GMAT (General Mission Analysis Tool). It is quite user friendly, has a number of tutorials, and has been used in spacecraft operations.


6

One thing that may be tripping you up is that the d term in the gravitational formula is the distance between the centers of mass of the objects, not the altitude above Earth's surface. The other thing to keep an eye on is your units. The big G gravitational constant is ~6.67 x 10-11 m3 kg-1 s-2; if you're using that value, make sure you're consistently ...


6

callhorizons is depricated now and refers to the python library astroquery which now seems to be the way to go. astroquery (GitHub, readthedocs) is "an astropy affiliated package that contains a collection of tools to access online Astronomical data. Each web service has its own sub-package.", where making Horizons queries is just one of many options. It's ...


4

I used the paper Wavelength dependency of the Solar limb darkening for solar limb darkening data. It uses the following model for the normalized brightness distribution across the disk of the Sun: $$ I(\mu)=1-u(1-\mu^\alpha) $$ Here, $\mu$ is the normalized distance from the limb; when far from the Sun, it can be expressed in terms of the normalized ...


4

The planet calculator lists a J2 of $0.001960454$ for Mars, higher than the Earth's $0.001082627$. That makes sense, as Mars has a smaller mass, but still approximately the same rotation rate. That means achieving a sun-synchronous around Mars is slightly easier than around Earth. However, MOM is not in such an orbit.


4

Change the "Table Settings". You want to select reference plane: Earth mean equator and equinox of reference epoch reference system: ICRF/J2000.0


4

Your variable root is of type IAgStkObjectRoot. If you search the Programming Interface Help, there are five save related methods for this type. These include Save() and SaveAs() So the easiest implementation would be: root.Save() which will save the scenario in the Documents\STK folder. If you want to control the specific location to save to you can try:...


3

A TLE describes the orbit of a body at a single reference point in time, which is called the epoch. It is straightforward to extrapolate the position of the object for some time forward or backward from that snapshot, but beyond that, limitations of the propagation model cause errors to grow, and the position of the object cannot be accurately estimated. ...


3

Should I actually be taking the JPL's advice to heart when it says, "These mean orbital parameters are not intended for ephemeris computation."? When you request orbital elements from Horizons, it does not return those mean orbital elements. It instead returns osculating orbital elements. The conversion between Cartesian states (position and velocity) and ...


3

Full disclaimer: I'm the author and main developer of poliastro. In poliastro there are several perturbations already defined, and among them you have zonal harmonics, Solar pressure, and the gravitational effect of the Moon. You can see the full list of perturbations here: http://docs.poliastro.space/en/latest/api.html#module-poliastro.twobody....


3

If I understand your question correctly, you might be able to use the location search query option in the API to get content for a particular rectangle specified by the latitude and longitude of the opposite corners. From the API docs: -c <coordinates i.e.: lon1,lat1:lon2,lat2> : coordinates of two opposite vertices of the rectangular area of ...


3

I just ran it, and mine look pretty much like those in the paper. See some coordinates at the bottom. Here are some {x,y} coordinates at the times in the left column: 0. {1.,3.} {-2.,-1.} {1.,-1.} 5. {2.46917,-1.22782} {-2.2782,-0.20545} {0.34106,0.901049} 10. {0.77848,0.141392} {-2.02509,0....


3

This might help to get you started. It's just a 1D radial solver, but you can play with the math. I included a 3D version of the derivative function to show one way to make the acceleration a vector in NumPy. Don't forget to add the rotation of the earth. The idea about starting on top of a mountain like Mt. Kilimenjaro is worth exploring for sure. I just ...


3

I'll try answering your two questions simply first. If these responses are too simple or miss the mark, let me know, and I'll edit the response. 1) What are the state propagation vector and State Transition Matrix (STM)? The state propagation vector is simply the position & velocity at a given time. The STM is a matrix that captures the sensitivity ...


3

From the point you are, you need to: Calculate the XYZ coordinates of your ground station Find the line in space between the satellite and the ground station Find the XYZ coordinates of the point at the intersection of that line with the ellipsoid defined by all the points with elevations of 300 km Find the latitude and longitude of that point. For (1) you ...


2

The State Transition Matrix (STM) The STM is a linearization procedure of a dynamical system. It can be used for any non-linear dynamical system and is used to approximate the dynamics of a system over short period of times. In astrodynamics, it is used especially for statistical orbit determination (stat OD) and the circular restricted third body problem (...


2

@Hohmannfan's answer states MOM is not in a sun-synchronous orbit. I just though I'd add some math to that. Using the equation for rotation of ascending node posted by @MarkAdler, I calculated the delta_OMEGA - how much the ascending node rotates in one year, for two cases: earth LEO and mars MOM. For earth LEO (400km) I get a little more than 97 degrees, ...


2

There is one now! I've just run across the python package callhorizons in github and Python Package Index. There is more information in readthedocis.io which helps explain how to do queries if you are looking for asteroids/minor bodies, for which there are zillions and the names can be people's name, or alphanumerics. I'll try to test it further and update ...


2

You may want to use Sentinelsat, which is an open source Python library to support searching, downloading and retrieving the metadata of Sentinel satellite images from the Copernicus Open Access Hub. It offers both an easy-to-use command line interface as well as a powerful Python API. Sentinelsat can be installed with pip and is available from here: https:...


2

Computing the angle between two vectors is going to be difficult if you first transform their x, y, and z coordinates into angles, because you'll then need to dive in the formulae of spherical trigonometry. Skyfield natively considers all positions to be x,y,z vectors, and it's often easier to compute if you leave them as "position" objects until you're ...


2

note: This answer addresses the question directly: How to calculate cone angle between two satellites given their look angles? If you need to use the look angles, this is a good way to do it. This better answer explains to the OP that if you are using Skyfield, that you should not use the look angles but instead use the coordinates in their original form....


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