Very cool discussion
Sent via the Samsung Galaxy S21 5G, an AT&T 5G smartphone Get Outlook for Androidhttps://aka.ms/AAb9ysg ________________________________ From: Nico Janssen hamsat@xs4all.nl Sent: Friday, July 22, 2022 4:25:48 PM To: Daniel R. Marlow marlow@princeton.edu; Burns Fisher wb1fj-bb@fisher.cc Cc: Ashhar Farhan farhanbox@gmail.com; wayne.greene489@gmail.com wayne.greene489@gmail.com; Joseph B. Fitzgerald jfitzgerald@alum.wpi.edu; AMSAT BB amsat-bb@amsat.org Subject: [AMSAT-BB] Re: Ten Russian cubesats to be deployed from the ISS
What actually happens in real life when a satellite is released from the ISS is the following.
The satellite is pushed, at a relatively low velocity, towards the rear of the ISS (i.e. opposite to the flight direction) at a certain angle below the horizon. This is done to prevent the satellite from colliding with the ISS in a later orbit. Because using this maneuver the satellite will lose energy, when compared to the energy the satellite had when it was still attached to the ISS. As a result, the satellite will start falling to a lower orbit, and therefore move away from the ISS. Additionally, the satellite has a higher drag factor, causing further loss of energy. So the satellite will soon be in a lower orbit, resulting in a higher velocity than the ISS. Therefore the satellite will get ahead of the ISS within days and move away from the ISS further and further. And that is when you need to start using separate TLEs for the satellite.
73, Nico PA0DLO
On 22-07-2022 22:17, Daniel R. Marlow wrote:
Hi,
The analysis is idealized (assume that the cow is a sphere) and assumes zero attraction between the ISS and the Cubesats. It also neglects drag forces and possible effects of the Moon, Sun, and other planets.
The basic idea is that one can think of an elliptical orbit as being a radial oscillation about a nominal circular orbit. It can be shown* that the period of the radial oscillation is equal to the orbital period (if that weren’t the case, elliptical orbits would not be “closed.”). From the point of view of an observer on a platform that is undergoing the circular orbit (we will assume this for the ISS), the Cubesat appears to move back and forth between a slightly lower and slightly higher orbit. It moves a bit faster when it is at its lowest point, and thus gets ahead of the ISS. When it is at its highest point, it moves slower and falls backward. The net effect is the aforementioned elliptical orbit.
73, Dan K2QM
* If there is interest, I can probably dig up my old notes on this problem.
From: Burns Fisher wb1fj-bb@fisher.ccmailto:wb1fj-bb@fisher.cc Sent: Friday, July 22, 2022 3:56 PM To: Daniel R. Marlow marlow@princeton.edumailto:marlow@princeton.edu Cc: Ashhar Farhan farhanbox@gmail.commailto:farhanbox@gmail.com; wayne.greene489@gmail.commailto:wayne.greene489@gmail.com; Joseph B. Fitzgerald jfitzgerald@alum.wpi.edumailto:jfitzgerald@alum.wpi.edu; AMSAT BB amsat-bb@amsat.orgmailto:amsat-bb@amsat.org Subject: Re: [AMSAT-BB] Re: Ten Russian cubesats to be deployed from the ISS
This is awfully interesting! Does the analysis assume a tiny amount of gravitational attraction between the ISS and the cubesat?
I think we are pretty sure that when multiple cubesats are released from a single P-POD one a ride-share rocket they have slightly different velocities and even if they stay in ~the same plane and altitude, they do separate in time. Just wondering how that all fits. (I suppose one difference is that the P-POD carrying stage will like change its orbit after the release).
Thanks!
On Fri, Jul 22, 2022 at 1:08 PM Daniel R. Marlow <marlow@princeton.edumailto:marlow@princeton.edu> wrote:
Hello,
A standard exercise in classical mechanics is to show that when an object is released in the right way from a satellite that is in a circular orbit, that object can end up appearing to orbit the main satellite. The shape of the orbit as seen in the reference frame of the main satellite is an ellipse. Unlike normal Keplerian orbits, where the attracting mass is at one focus of the ellipse, the main satellite is at the geometric center of the elliptical orbit.
73,
Dan K2QM
P.S. Normally the sub satellites are taken to be beer cans, but this analysis should also work for Cubesats.
From: Ashhar Farhan <farhanbox@gmail.commailto:farhanbox@gmail.com> Sent: Friday, July 22, 2022 11:57 AM To: wayne.greene489@gmail.commailto:wayne.greene489@gmail.com Cc: Joseph B. Fitzgerald <jfitzgerald@alum.wpi.edumailto:jfitzgerald@alum.wpi.edu>; AMSAT BB <amsat-bb@amsat.orgmailto:amsat-bb@amsat.org> Subject: [AMSAT-BB] Re: Ten Russian cubesats to be deployed from the ISS
When a satellite is dispensed from a mothership like the ISS, the orbit cant really go too far away due to the nature of orbital mechanics. The iss and the cubesat orbits will have to intersect at least twice. Is there a more precise modeling of this?
On Fri, Jul 22, 2022, 9:19 PM Wayne Greene <wayne.greene489@gmail.commailto:wayne.greene489@gmail.com> wrote:
ok. I'll try the ISS predictions, then. I wasn't able to find anything in space track. Of course, I might have been doing something wrong with my searches.
On Fri, Jul 22, 2022 at 11:32 AM Joseph B. Fitzgerald <jfitzgerald@alum.wpi.edumailto:jfitzgerald@alum.wpi.edu> wrote:
Regular ISS predictions will be pretty accurate for several days. They were released by hand so the delta-V imparted will be pretty low.
de KM1P Joe
--
Wayne Greene
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