# Tag Archives: space

## Gravitational Tricks: Lagrange Points and Orbiting at Puzzling Speeds

The orbital path of ISEE3 from launch to near present.

Last time I talked about a team trying to capture and reuse the ISEE3 satellite (here).  The team has received lots of telemetry lately, determined the rotation speed of the satellite, and even had an amateur radio operator receive the satellite!  While all of this is going on, they must rapidly plan out what orbit they wish to enter.  The most discussed orbit is termed ESL1, the Earth-Sun system Lagrangian point #1.  Lagrange points an interesting phenomena that I thought worth a short discussion.

When we think of orbits, traditionally we consult Kepler's laws.  These "laws" are 3 simple rules that were written down between 1609 and 1619 by Johannes Kepler.  I won't discuss them at length, because there are already many great sources to learn about Kepler's Laws and their application.  The thing we want to draw from them is that an object orbiting closer to the Sun (say Venus), will have to travel faster to satisfy the laws of nature.  In doing so it will orbit the Sun more times than the Earth will in the same amount of time.  Venus will in fact orbit the sun 1.6 times during 1 orbit of the Earth!

Let's say we place a satellite far away from the Earth, between the Earth and sun.  the satellite will orbit slightly faster than the Earth.  Over a period of time it will be on the opposite side of the Sun and we won't be able to communicate.  Eventually it will come around and lap the Earth! This isn't desirable, but we can use Lagrange points to solve this problem.

The simple laws of orbital mechanics that we have considered thus far are only valid for a simple problem with two objects (Earth and Sun or Earth and Satellite).  We have we three bodies though, the Earth, the Sun, and the satellite! Three body problems are generally sticky to solve, but we have an advantage.  The mass of a satellite is small compared to the mass of the Earth and the mass of the Sun (unless it's the Death Star).   We can ignore the small mass of the satellite as solve what is known as the restricted three body problem.  There are a few interesting points in space, the Lagrange points, at which the gravitational pull from the Sun and Earth are superimposed on each other to give the satellite the same orbital speed as the Earth!

The L1 point is where ISEE3 may end up, so let's look at it.  The satellite will be above the Earth at an altitude of 1.5 million km (932,000 miles), towards the Sun.  At this point, the two body mechanics say that the satellite will orbit the Sun faster than the Earth.  Adding in the complications of the three body problem, we see that the gravitational tug of the Earth towards the Earth,  away from the Sun is canceling out just enough of the Sun's pull to make the satellite orbit at the same angular speed as the Earth.  How useful!

There are other Lagrangian points as well (L2-L5), but we won't discuss them here, other than to say that a similar explanation can be given for each.  L4 and L5 are particularly interesting because they are inherently stable and hence lots of objects get caught there.  There are objects in Earth-Sun L4/L5 and Earth-Moon L4/L5.

Lagrange Points of the Earth-Sun system (Image: Wikipedia)

Generally satellites are placed in a small orbit around the L1 point for several reasons, including that it isn't inherently very stable.  The ISEE3 team will have to execute a rather complex series of maneuvers to get to L1 again, using the pull of the moon and making a very close pass that comes within 10's of km of the surface of the moon.  Time is of the essence, as the longer the wait the more they must change the speed of the craft (referred to as Delta V in the engineering jargon).  The ship only has about 150m/s of Delta V left before it runs out of fuel.  It'll take up to 1/3 of that to reposition the satellite, depending on how long the team must wait.

That's the quick and dirty view of Lagrangian points.  I hope this was interesting and helps you understand space exploration, or your addiction to Kerbal Space Program a little more!

## Reviving a Piece of the 1970's: ISEE-3

There's been a decent buzz in the space and tech communities about the "ISEE-3 Reboot Project", so I thought it would be worth mentioning here and pointing out some of wonderful techniques they are using to revive a satellite from almost 40 years ago.

The ISEE-3 satellite is one of three satellites that made up the International Cometary Explorer (ICE) program.  There were some interesting orbital things done with this satellite after its launch in August of 1978.  It was also the first spacecraft to go through the tail of a comet!  As with all missions, this one came to an end and the satellite was not head from since 1998.  The equipment to talk to the satellite was removed and it was considered to be out of service.

ISEE-3 sits in a heliocentric orbit, meaning that orbits the sun, not the Earth.  We knew that ISEE-3 would make another stop by our planet in 2014 when it was parked in this orbit in 1986 (from what I can tell anyway).  A group of citizen scientists started the ISEE-3 Reboot project, crowd funded on the internet.  They got permission to take over the satellite and intend to use the Moon's gravity and a rocket burn to send it on another mission.  If the window of June is missed, the satellite will probably never be heard from again.

The team was able to contact ISEE-3 on May 29 using the Arecibo observatory radio telescope.   The craft was commanded to transmit engineering telemetry, basically a health screening of the systems.  The team is currently busy decoding the data (streaming in at 512 bits/sec) and planning how they will execute the rocket burn.

The team is running out of an old McDonalds at the NASA Ames Research Park, the makeshift mission control has been termed "McMoons" after hosting previous space based projects.

That's all for now, but stay tuned to the team's website for updates and I'll be keeping up with the progress as well.  This is just another incredible example of how advanced hardware and software that has become relatively cheap can allow a group of savvy citizens to accomplish incredible feats!  Way to go folks!

## KickSats - An Interview with Zac Manchester

Another AGU related post, but this time one that offers a future opportunity for participation! While walking around the vendors areas I approached a space company and began talking with a student at their booth. He turned out to be Zac Manchester, the main driver of the KickSat campaign. We chatted for a bit and I thought this would make a great post as well as letting you know about an upcoming opportunity to help telemeter data down.

Zac Manchester showing off an example satellite at the AGU Fall Meeting.

You can find out some about the project from KickSat.net. After the meeting Zac was kind enough to answer some questions for the blog. There will be a future post as well where I'll share my personal ground station setup and then posts during reception of the data in Feburary. It's fun to see these tiny satellites that are just a printed circuit board with a solar cell and no battery. Amazing design and great use of a Texas Instruments microchip with a built in radio! Zac actually repurposed these chips as they are designed to be used in wireless key entry systems in cars. Fantastic!

What inspired you to start the KickSat program?
Mostly desperation. Our research group at Cornell has been working on
"ChipSat" scale spacecraft for a number of years and we got to a point
where we felt we were ready to actually fly some in space. We were
able to get a free launch through a NASA program called ELaNa, but we
still needed some money to build the flight hardware. KickStarter was
still pretty new at the time (2011), but I had heard of it through
some friends. After thinking it over a lot and not really having many
other options, we decided to go for it.

What was the most difficult challenge during the project?
The most difficult technical challenge was probably the communications
system. We're trying to simultaneously receive signals from over 100
tiny satellites, each with only about 10 mW of power, from 500 km
away, all on a very low budget.

How will the satellites be deployed and where can we find tracking data?
The Sprites will be deployed out of a 3U CubeSat "mothership" (called
KickSat), which is being launched on a SpaceX Falcon 9 in late
February or early March. The Sprites will be deployed 7 days after
launch vehicle separation and we will have tracking data available on
our website (kicksat.net).

When is launch?
Officially February 22, 2014, but that will likely be subject to delays. This is now set for March 16, 2014.  You can check for updates by looking for spacecraft "SpaceX CRS 3" on  SpaceFlight Now.

How long will the satellites be in orbit?
KickSat, the 3U CubeSat "mothership" will stay in orbit for a few
months, while the Sprites will reenter in a few days, probably less
than a week, after they are deployed.

How can educators and radio operators receive the data? How should be send in any data we receive?
We'd love to have participation from as many radio amateurs as
possible. Information on how to set up a ground station, receive
signals, and submit recorded data will be posted on kicksat.net in the
coming weeks.

That's it! Thank you for reading and be sure to check out any follow up posts.  I'll be setting up my ground station over the next week.