26 votes
Accepted

How did two satellites end up in almost the same orbit except moving in opposite directions?

How? Simple, because they launched into those orbits. Why? Well, first, let me explain what their orbits actually are. IRAS (13777) and GGSE-4 (2828) are both in high-inclination orbits, 70° and 99°...
Anton Hengst's user avatar
  • 10.7k
21 votes
Accepted

Is it normal for the US Space Force to warn companies about a possible collision (conjunction)?

Space Fence is what our current tracking system is called. This article claims that some companies and countries have an arrangement to receive tracking data, but few details. It appears that this in ...
Harabeck's user avatar
  • 338
13 votes

Is it normal for the US Space Force to warn companies about a possible collision (conjunction)?

It's routine, and done as a service for the space community at large. Companies doing official business with the U.S. Government can get access to a variety of additional services, but the basic ...
Ryan C's user avatar
  • 7,942
9 votes
Accepted

Has an astronaut ever seen another object in LEO pass by that wasn't mission-related?

It turns out it might be very common for astronauts on the ISS (or previously the MIR) to spot satellites. This is the distribution of the number of satellites in LEO for different altitudes As you ...
Swike's user avatar
  • 2,501
7 votes
Accepted

What was the relative velocity of Kosmos-2004 and the ChangZheng rocket stage at their closest aproach?

LeoLabs tweet: We are monitoring a very high risk conjunction between two large defunct objects in LEO. Multiple data points show miss distance <25m and Pc between 1% and 20%. Combined mass of ...
uhoh's user avatar
  • 149k
4 votes

What are these squiggly lines in Jonathan McDowell's tweets about Yunhai-1?

From McDowell tweet of Aug. 15th, 7:17AM 37 debris objects (green) have been cataloged so far from the breakup - there are likely to be more. the most obvious interpretation is that the green lines ...
Ng Ph's user avatar
  • 2,724
4 votes
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What does "MSR" represent in the context of this predicted satellite conjunction?

MSR is one of LeoLab's radar stations (LeoLabs being the people who tweeted about the potential collision, a company whose busines is monitoring satellites). It lives in Midland, Texas, and as such is ...
Starfish Prime's user avatar
4 votes
Accepted

Algorithmic methods or techniques to find conjunctions in high N Keplerian element ensembles?

Propagating $N$ objects and checking $N(N-1)/2$ distances at each small time step is indeed computationally inefficient to the point of being impractical. If I recall correctly, there are currently ~...
LeWavite's user avatar
  • 701
3 votes

Has an astronaut ever seen another object in LEO pass by that wasn't mission-related?

Really late additional, not to distract from the answer already given: William Francis "Bill" Readdy, Flight Engineer and Flight Specialist on STS-42, carrying International Microgravity ...
blobbymcblobby's user avatar
3 votes

Algorithmic methods or techniques to find conjunctions in large ensembles of state vectors?

Let's say you want to do something "reasonable", like collecting second-by-second conjunctions for a hundred year period, for all the objects you can get your hands on state vectors for (a ...
SE - stop firing the good guys's user avatar
3 votes
Accepted

Calculating the radial, in-track and cross-track distances

It looks like you're working from the JSpOC Spaceflight Safety Handbook for Operators (https://www.space-track.org/documents/JSpOC_Spaceflight_Safety_Handbook_For_Operators.pdf). In this case they ...
CoAstroGeek's user avatar
  • 1,919
3 votes

What is the probability of impact?

The equation for the distance between the two objects is simply the magnitude of the vector between their positions. Numerical root-finding is made easier by knowing the analytic derivative, which is ...
Ryan C's user avatar
  • 7,942
2 votes

What is the probability of impact?

The document https://www.space-track.org/documents/How_the_JSpOC_Calculates_Probability_of_Collision.pdf was written and posted in 2016. It discusses the process for the computation of probability of ...
Ken Kopke's user avatar
2 votes

What is the closest intentional separation achieved by two satellites?

How About Half a Kilometer The GRACE mission was mentioned in a very complete answer by @Rob (mentioned as GRACE-FO, which is the current mission replacing GRACE). However, unmentioned is the fact ...
ben's user avatar
  • 1,156
2 votes
Accepted

What is the closest intentional separation achieved by two satellites?

There's a disadvantage to placing satellites too close together for no reason, if struck by a micrometeoroid pieces of both the space debris and satellite pose a danger to its companion; it's ...
Rob's user avatar
  • 3,276
2 votes

Has a cubesat ever caused a problem for another spacecraft? Examples? Close calls?

You mention the only one I have heard of: Question: Has a cubesat ever caused a problem for another spacecraft? M-Cubed was launched in the Fall of 2011 on the NASA's third Educational Launch of ...
blobbymcblobby's user avatar
1 vote
Accepted

Closest approach between the JWST launch vehicle and Santa Claus's sleigh?

There was never any chance of conjunction! The launch happened at "lunch time" in western Europe, at about 12:20 UTC on 25-Dec-2021. Santa would be in places where it was late at night or ...
uhoh's user avatar
  • 149k
1 vote

Closest approach between the JWST launch vehicle and Santa Claus's sleigh?

By the time JWST launched, Santa should have been long since done with his errands in that part of the world. And JWST was way above Santa's track PDQ!
FlaStorm32's user avatar
1 vote

How often does Mars appear at the horizon in our sky?

Twice daily, as the earth rotates. This occurs no matter where you are. The time between transitions varies on the observers location. Close to the equator, it is approx 12hrs between transitions, ...
Innovine's user avatar
  • 4,625
1 vote

What is the closest intentional separation achieved by two satellites?

If the intention is to get really close, rendezvous is possible. Though is common to just take them up together. I.e: LISA pathfinder has 3 separate bodies that have been held close for prolonged ...
drjpizzle's user avatar
  • 349

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