16 votes
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What was the globe instrument in Vostok 1?

From russian wikipedia: Another instrument helped to the pilot to decide when to start manual operation to return to Earth - it was a small globe with a clock mechanism, which shows the (calculated, ...
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8 votes
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Can Keplerian elements from TLEs be used without SGP?

Not without a lot of error. The elements in the TLEs are "mean elements", not "osculating elements". i.e. although they have the same names as the Keplerian elements, they are not really measuring ...
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  • 9,949
7 votes
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How does the Orbit Determination Accuracy depend on the number of measurements?

There are several aspects playing a role here: first of all, every measurement has a certain random inaccuracy. Ask ten people to measure the size of an object with the best precision possible and you'...
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  • 13.3k
7 votes
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Is it possible for amateurs to determine the orbit of satellites

Yes it absolutely is! I'm writing this to make this clear that your question is squarely on-topic. Here is an example of a (very experienced) amateur, Scott Tilley, both finding and determining the ...
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  • 148k
6 votes
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How is real position of probes orbiting other planets measured?

Here is a good tutorial on the navigation of deep space vehicles. The two main data types used are two-way Doppler (using an atomic clock reference at the DSN station, with the frequency locked to ...
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  • 57.7k
5 votes

How do you compare a simulation with a fitted orbit?

Comparisons between predicted orbits (numerically integrated) and fitted orbits (from tracking data) are usually done in an inertial reference frame, such as ICRF or Mean of J2000. Within these ...
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4 votes

Spacecraft position determination

As I understand tone ranging is one of the technique used to determine satellite range from the earth station. In this case the position along the line of sight is being determined. How the position ...
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  • 65.5k
4 votes
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Tracking Arc and Time for Precise Orbit Determination

Is there any such record of distinct tracking time required in missions? I was unable to find any mission specific examples of utilized tracking time following a TCM or otherwise. I believe this is ...
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  • 1,374
4 votes

Why are Keplerian elements used in TLEs instead of Cartesian state vectors?

Propagating a state vector seems easier, you just account for the gravity, change the velocity and update the position. You described the symplectic Euler method (aka semi-implicit Euler method, ...
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  • 65.5k
4 votes
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Significance of measure of dispersion in Orbit determination output

It's all about choosing how much tolerance you have for uncertainty. The more sigmas you use, the higher your confidence becomes that the object is within that many standard deviations of the ...
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  • 5,627
4 votes

How significant is orbit propagator choice/error when considering a year-long satellite coverage simulation, and which is the most appropriate?

Propagating for an entire year is extremely difficult to get right. There are ways to do it, but you should not attempt to rederive or reimplement them yourself. Before I describe them, however, I ...
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  • 5,627
3 votes
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How do I obtain geocentric position vectors at three successive times before I use Gibbs' method?

This is my tentative answer to my own question (based on suggestions in the comments). Obtaining three different geocentric position vectors (km) over 10 minutes ...
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3 votes
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Orbit Determination of ISS just with a telescope and a watch?

As the answer to that question states: In general, an epoch time and six scalar values that completely represent the state at the epoch time are needed. The six values you can choose as you like, as ...
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  • 13.3k
3 votes
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Can the TLE epoch be listed as in the future? How?

I thought this question has been answered here before, and that the answer went into some detail about why this is done from time to time, but I can't find any trace of that now. The epoch could, ...
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  • 148k
3 votes
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How significant is orbit propagator choice/error when considering a year-long satellite coverage simulation, and which is the most appropriate?

I'm not an expert and this is not an expert answer, but these points may be helpful. Don't even think about using SGP4, per my comments below this question and Wikipedia it's a circa 1980's clever ...
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  • 148k
3 votes

Is it possible to update an existing TLE using new data?

Is it possible to update an existing TLE using new data? Of course it is. How do you think TLEs are updated? That said, it's not easy. You'll need to Compute the Jacobian of your new data with ...
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  • 65.5k
3 votes

Is it possible for amateurs to determine the orbit of satellites

Here's amateur listener Sven Grahn watching the launch of Chang'e-1 and boost to deep space in 2007, from Tracking Chang’E-1 from Sweden The map in the last one certainly doesn't look like Stockholm, ...
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  • 148k
3 votes
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Orbit Propagator with J2 perturbation has larger error compared with simple 2 body Propagator

Thanks everyone for your help and advice! After some troubleshooting, I found out that the large position error of the "orbit propagator with J2 perturbation" is due to the bad initial ...
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3 votes

Why are Keplerian elements used in TLEs instead of Cartesian state vectors?

For a body in orbit in 2-body scenario, for Keplerian elements only a single variable (true anomaly) changes over time. For Carthesian the whole state vector is in constant flux. When working with ...
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  • 52.6k
3 votes

Onboard propagator in satellites SGP or J2

Many satellites do not have any position or velocity measurements. Time tag tables including satellite state, magnetic and sun vector are been uploaded from the ground and the satellite uses it for ...
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  • 958
3 votes

Onboard propagator in satellites SGP or J2

The first question you need to ask yourself is the following: does the spacecraft need to know its own position? Many, if not most, spacecraft do not need that information. The ground team simply ...
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  • 5,795
3 votes

Can Keplerian elements from TLEs be used without SGP?

The short answer is: its not clear**, however, if you have no independent measurements of your own then TLEs will have to do. If you have some comparable case where you have both your own ...
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  • 8,918
2 votes

What was the globe instrument in Vostok 1?

Two variants of the Globus retained in my collection - in the foreground from Voskhod, in the background installed in the Soyuz TM panel is the later version)
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2 votes

Spacecraft position determination

If you got the position along the line of sight, you can measure the elevation and direction angle of the line of sight too. You have one distance and two angles and using a coordinate transformation ...
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  • 1,694
2 votes

Can the TLE epoch be listed as in the future? How?

From Space-Track.Org FAQ TLEs can contain future epochs. About 20 satellites are categorized as "multi-day objects" because their period is so large. Consequently, our data provider ...
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  • 163
2 votes
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Can I convert from TEME to Keplerian orbital parameters?

ECI doesn't have an actual reference time, it's just an arbitrary one that is useful. It works well for rockets and things with limited lifespans, but for satellites it is a bit trickier. As Celestrak ...
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  • 119k
2 votes

Can we determine the position of an artificial satellite using Kepler's parameters?

Short answer, yes. Long answer: There are 6 keplerian orbital elements (but note that these parameters are not the only way to describe an orbit). Semi-major axis, eccentricity, inclination, argument ...
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1 vote

What are N and D variables which take part in this Gibbs' method/algorithm for orbit determination

From the page you linked, it looks like N and D are just intermediate values used to make the following equations shorter and more readable.
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  • 711
1 vote
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Calculated Classical Orbital Elements of the ISS seem to differ from the actual ones

(Ok, this is my attempt of answering my own question based on the suggestions in the comments, full credits to @uhoh and @David-Hammen) The main issue As pointed out by @uhoh, the main issue here is ...
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1 vote

How do you compare a simulation with a fitted orbit?

First, you need to make sure both results (simulation results and laser ranging data) are converted into the same coordinate system. This is usually chosen as an inertial frame, like ECI. You can ...
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