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Posts Tagged ‘Orbits’

Ephemeris: 11/12/2024 – SpaceX uses Cargo Dragon to change orbit of the ISS

November 12, 2024 Comments off

This is Bob Moler with Ephemeris for Tuesday, November 12th. Today the Sun will be up for 9 hours and 40 minutes, setting at 5:17, and it will rise tomorrow at 7:37. The Moon, halfway from first quarter to full, will set at 4:39 tomorrow morning.

After the last SpaceX cargo mission arrived at the International Space Station, they used the thrusters on the SpaceX capsule to raise the orbital space station a little bit as a test. SpaceX capsules dock at the forward end of the space station according to direction of travel so in order to boost the station’s orbit they had to flip the station around so that the docking port was at the rear before they could apply the needed thrust. When thrust is applied to an object in orbit the effect of the change occurs mostly at the opposite side of the orbit. In order to permanently raise or lower an object’s circular orbit one must make 2 adjustments 180° away from each other. This is the essence of the Hohmann Transfer Orbit, proposed by German scientist Walter Hohmann in 1925.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). Times will be different for other locations

Addendum

Hohmann Transfer Orbit
Hohmann Transfer Orbit (2) moving, in this case. from one circular orbit (1) to a higher one (3). Moving from point a to point b. The triangle symbol is the Greek capital letter delta, which means change. It reads as delta V, or change in velocity. Image credit: Leafnode based on image by Hubert Bartkowiak in Wikimedia Commons with a and b points added by this author.

Categories: Concepts, Ephemeris Program Tags: , , ,

Ephemeris: 07/11/2024 – Low energy routes to get to the Moon

July 11, 2024 Comments off

This is Ephemeris for Thursday, July 11th. Today the Sun will be up for 15 hours and 19 minutes, setting at 9:27, and it will rise tomorrow at 6:09. The Moon, 2 days before first quarter, will set at 12:26 tomorrow morning.

Back in the Apollo days when we sent people to the Moon, the trip out was only three days. The latest generation of unmanned probes to the Moon sent by the United States and other countries can take days, weeks, or even months to reach the Moon, so what’s going on? These are robot probes, needing little power. Humans however are high maintenance. Even when they’re doing nothing they are breathing, eating, and using resources. So when humans are aboard you have got to get there fast. Also, many of these probes are CubeSats, no bigger than a breadbox*. They must get into orbit of the Moon with very little thrust other than that of the rocket that launched them. They can go out as far as a million miles away before falling back to the Moon.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT–4 hours). They may be different for your location.

* OK, I’m an old guy, the modern size comparison would be a microwave.

Addendum

An example of a low energy trajectory to the Moon
Here’s an example of a low energy trajectory to the Moon taken by the two Grail spacecraft back in 2011. The two spacecraft were launched on the same rocket, a ULA Delta II vehicle and were sent out in the direction of the Sun and maneuvered to separate themselves so that they would arrive at the Moon a day apart. This was done by various trajectory correction maneuvers. The spacecraft headed out toward the Earth Liberation Point 1, which is also called the Sun-Earth Lagrangian point 1 or L1. This is a way to get to the Moon with a minimum of additional energy to drop into orbit around it. It took the spacecraft about 3 1/2 months to arrive at the Moon. The word open refers to the trajectory at the opening of the several day long launch window. Credit NASA/JPL.

Categories: Concepts, Ephemeris Program, Space Flight, The Moon Tags: , , , ,