Tag Archives: NASA

Gravitational Tricks: Lagrange Points and Orbiting at Puzzling Speeds

The orbital path of ISEE3 from launch to near present.

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)

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.



The part of this that I find amazing is the role that software defined radio is playing.  Software defined radio (SDR) is a way to use software to emulate radio equipment.  With a small USB stick I can receive many different kinds of radio signals and decode them, something that would have required racks of equipment a few years ago.  This team is using a radio termed the "USRP" that allows them to transmit and receive.  I've written about them before (here) and have used them in research.  They are amazing little units and provide a unique learning opportunity.  (Maybe I'll post something about a radar we made with one of them as a demo!)  A photo tweeted by the team shows 2 USRP units and laptops hooked into the giant dish antenna at Arecibo.

Screen Shot 2014-06-02 at 12.51.08 PM


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!


Remembering Challenger: 28 Years


It's been 28 years since the Space Shuttle Challenger (STS-51-L) broke apart just over a minute after launch.  Disasters like Challenger and Columbia remind us that space exploration really is a complicated and risky business.  Should we stop because something is risky? Absolutely not, but we should also not let such things become routine and fall out of the public view.

Remembering the Challenger Crew

The NASA family lost seven of its own on the morning of Jan. 28, 1986, when a booster engine failed, causing the Shuttle Challenger to break apart just 73 seconds after launch.

In this photo from Jan. 9, 1986, the Challenger crew takes a break during countdown training at NASA's Kennedy Space Center. Left to right are Teacher-in-Space payload specialist Sharon Christa McAuliffe; payload specialist Gregory Jarvis; and astronauts Judith A. Resnik, mission specialist; Francis R. (Dick) Scobee, mission commander; Ronald E. McNair, mission specialist; Mike J. Smith, pilot; and Ellison S. Onizuka, mission specialist.


Earthrise - 45 Years Ago Today

Earthrise Photograph

The famous "Earthrise" photograph.

On December 24, 1968 one of the most powerful photographs of our time was captured. Today being the 45th anniversary of this event, I thought a brief look back would be fitting. The crew of Apollo 8 (Borman, Anders, and Lovell) were just finishing their fourth lunar orbit when they saw an awe inspiring sight. Due to a roll maneuver being executed by the spacecraft, the Earth came into view out of the window. As the astronauts were just coming around from the far-side, the Earth was rising over the lunar terrain! This was a sight that nobody had seen before. There was a scramble for film, first a black and white photograph, then finally a color photograph as the capsule rotated further and the event came into view of another window. Listening to the crew conversation is very interesting as they hurry to photograph the event with their Hasselblad 500EL. The "Earthrise photo" is more officially known as NASA photo AS8-14-2383.

The scientific visualizations team from NASA have done a fantastic job putting together a short video showing the events that transpired with syncronized crew voice recordings. By using photos from the recent Lunar Reconnisance Orbited (LRO) and a timed camera on Apollo 8 they have even determined the exact orientation of the spacecraft during these events. I highly recommend watching it! This greatly reminds us of the sentiment Eugene Cernan expressed later in the program: "We went to explore the moon, and in fact discovered the Earth."

Building a Fluxgate Magnetometer - Part 1 (and NASA)

Today I want to discuss the first steps in building a simple fluxgate magnetometer for a classroom demonstrator.  Originally this post was going to be a wrap up of NASA work and the magnetometer would come later, but I'm still waiting on my presentation to clear export control so I can post it.  As soon as it does, I'll put it up along with a short article.

This semester I'll be the TA for 'Global Geophysics', mostly doing lab instruction/writing.  After some thought I decided that students need more hands-on classroom geophysics, which is difficult to do.  By its nature geophysics is an outdoor activity with normally expensive instruments.  The instruments are often viewed as a mysterious black box that spits out numbers used to make a map.  This must change.  With a proper understanding of the instruments students will better understand errors in the data, how to troubleshoot in the field, and know why certain hardware limits exist.

The concept of a fluxgate magnetometer is pretty simple.  Rather than go into detail I'll refer you to this wikipedia article.  This is mainly to chronicle the construction so others can reproduce this (assuming we get a working model).  My design came from a physics lab at Brown University.  The instructions were vague in parts and I'll be taking some liberties as we go along.  This first article will cover construction of the coil and the driver circuit.

The fluxgate coil consists of a driver coil surrounding a soft steel wire, and a secondary coil to pickup signal surrounding the primary coil.  First I took 16ga annealed steel wire from Lowes and cut it to about 1m long, cleaned it, and made it as straight as possible.  Afterwards I wrapped close to 2000 turns of 22ga magnet wire (Radio Shack #278-1345) tightly along its length.  This was then bent in half making a 'U' and that was wrapped with close to 1000 turns of 26ga magnet wire. I used large wire because it will be more durable and I used different gauge wire since the enamel insulation was a different color allowing students to easily see the windings.

That's all there is to the coil.  To increase durability I will probably clear coat the coil and place it into a small acrylic tube so its difficult to bend or break.  The next step is to build a driver for the primary coil.  The Brown lab used a function generator.  Currently I don't have one, nor have I found a suitable cheap unit.  This meant improvising, and luckily Velleman makes a signal generator kit that is just about right.  It operates at 1kHz (the desired frequency for this project) and produces sine, square, triangle, and integrator waves.  The kit was pretty easy to build in just about an hour and works well as seen by the oscilloscope output below, but frequency stability is not phenomenal (especially when then unit is cold).  

Next a few amplifiers need to be designed and built.  The signal generator kit cannot pull the load of the coil, so a simple +/- 9V system will probably do.  The output will also need some kind of amplification.  The lab I found also uses a bandpass filter.  Once the amplifiers are working it will be time to decide if this is necessary and if I want to use an oscilloscope and hardware filters, or an ADC and display the waveform on a computer projector using software filters.  

NASA - Mission Control and Flying the Shuttle

Yesterday I was fortunate enough to go through the mission control facilities here at Johnson Space Center. There is historic mission control from the Apollo and early shuttle days, space shuttle control, ISS control, a training/overflow room, and back rooms. I'm going to share some pictures with you and summarize the setup of mission control and operations.

First we were in historic mission control. This is the famous room seen in the photos of the Apollo 11 landing and made even more well known by the movie 'Apollo 13'. The room is relatively small with a visitor viewing gallery. Each station or console was responsible for a system or set of systems such as guidance, navigation, control, CAPCOM (capsule communicator), etc. Every console has a set of loop buttons. These loops can be thought of as conversations. Say the thermal guys need to talk to attitude control (ADCO) and maneuver the spacecraft so it can cool or heat properly. They would punch up a loop and start talking. Controllers listen to many loops simultaneously, but only talk on one at a time. Eventually all decisions are at the discretion of the flight controller. When a decision is made the CAPCOM (the only person who actually talks to the spacecraft) relays the message.

A little known fact is that those controllers in the 'front room' are not the only personell working on the mission control day to day. There are many 'back rooms' surrounding the control center in which more systems specialists look at various sub-systems and aspects of operation. They report to the front room system manager who then reports to flight control. This design of control is still used today. In addition to subsystem back rooms there are also people like geologists in back rooms that would request astronauts look at certain areas/rocks when on the moon.

Shuttle mission control is now sadly quiet after the recent retirement of the space shuttle after a great 30 year run. I've posted pictures of the shuttle control room before, so I'll save the space here and move onto the International Space Station (ISS) control room.

The ISS control room is similar to shuttle control with one major exception. The ISS is flown from the ground. With the shuttle and Apollo astronauts actually flipped switches and punched up computer programs to fly the vehicle. The ISS astronauts are free to work knowing that their orbit is controlled by the ground. The orbit of the ISS is occasionally boosted to combat continual orbital decay. The orientation of the station is also changed for thermal, scientific, and debris avoidance. Much of the maneuvering is done by speeding up, slowing down, and rotating giant gyroscopes on the station. These moves require no propellant, but there are technical issues (that's for another time though).

There is also a training/overflow control area, but that area is currently undergoing a few remodeling projects.

On a side note I was able to fly the shuttle simulator before it is dismantled. We started at 10,000 ft. on landing approach. I came up just short of the runway the first time, but got it on the ground the second time (even if it wasn't a pretty landing).

NASA - What's New

Well a lot has happened since my first week down at NASA.  I've watched the final launch and landing of the shuttle with STS-135, visited historic and current mission control, watched a dry run of the desert rats program, and even got to shake the hand of robonaut!

The launch of the shuttle was amazing, even just watching it on the big screen with other employees cheering.  Once they were in orbit we recorded a wake up message to be played to them during one of the flight days.  The video is embedded below.  Skip ahead towards 1:13 and you'll see all of us.  I'm in a denim shirt near a guy in a bright red shirt.  We all went into work at 4AM to watch the landing, then went to Waffle House for some breakfast.

Morpheus still hasn't lit up since I've been here due to the fire investigation and more recently some RF interference issues.  Hopefully those are resolved soon and the tests can continue.  My work on writing a software package has shifted slightly and I'm writing a plotting package.  When I give my exit presentation in a few weeks I'll post it on here so you can get a more detailed idea of what is going on, but in general my software takes huge amounts of flight data and divides it up to plot it.  We are already using the software to look for what is causing some drift in the inertial navigation system!  I'll try to do better about posting more frequent, short updates over the next couple of weeks before I head back to Norman and the blog will likely go back to interesting scientific thoughts or updates on teaching.

NASA - Week 1

This week I began my work at NASA Johnson Space Center (JSC).  My job is to write software regression test protocols for the guidance, navigation, and control software on a lander prototype.  We normally refer to the software as the GN&C package.  It basically tells the flight computer and flight computer software (FCS) what to do as far as maneuvering the vehicle.

The vehicle I'm working on is called Morpheus and will with any luck be the next machine we place on the moon.  It may take some instrument up after a few more years, but only time and funding will tell.  Below is a picture of the lander with me for scale.

I encourage you to also follow the Morpheus blog from NASA (here).  Videos of tests will be posted there, but I'll also repost.  The first few tests the lander was tied down to the ground.  Then it was hung from a tether and allowed to ascend and land on its own.  Some of the tests worked well, but others had problems as is in the video below.  Most of those issues have been solved and we are now just working on some control lag problems.

More tests were planned very soon, but the rocket started a fire in the test field and we can not light the engine again until the investigate has cleared up, hopefully by early July.  Until we do more field tests I'm working in the NSTL (Navigation Systems Testing Laboratory) trying to do regression analysis.  In general fixing a bug in software can break other features.  When the software is flying a very expensive lander with around half a ton of explosive rocket fuel that is a very bad thing.  I'm using spacecraft simulation code to prove that certain changes don't cause issues with the flight and trying to develop software modification protocols that allow rapid updates.

The icing on the cake was really my first day when I happened to hear that Gene Kranz (the flight controller for many years, made famous in the movie 'Apollo 13') was speaking.  I attended his lecture and it was amazing.  He really has the passion that I love seeing in people.  Mr. Kranz was excited for what our generation can do, but concerned that we may currently lack the leadership to do it.  I agree completely with his statement and all of us in the room are striving to learn those vital skills that he talked about.  The Apollo missions would have never left the ground without leadership, teamwork, and persistance.  While we may have many times the computer power of the 1960's I'm worried we have fewer of these important personal qualities.

Constellation Cut?

With the release of the proposed budget science education saw a nice boost in funding, but science programs saw cuts. NASA was one of the most hurt agencies. This was simply upsetting as we know how weak we are as a nation when it comes to science. (I've often been scared when visiting a medical doctors office and hearing the doctors confession of barely making it through calculus one.)

Constellation was supposed to get space exploration back on our minds and provide more technological advancements. Many of the modern items we enjoy have their roots in the space program. Our technology has also advanced greatly since the 60's and 70's. The computer on the Apollo missions ran at a whole 2MHz and would shudder if it met a modern graphing calculator, or my iPhone which is over 300 times more powerful! (And about 69.9 pounds less in weight)
Please read, modify, and send the letter below to your representative! Unless you are also a student on a PhD track you might want to change that bit, but otherwise you could use it pretty much unmodified if you wish.