Dennis Wingo: : The ISEE-3 Reboot project is an effort to contact, evaluate, command, and place back into operation in an Earth orbit the International Sun-Earth Explorer #3 (ISEE-3) spacecraft. In 1978 the ISEE-3 spacecraft was launched as part of a trio of spacecraft to monitor and understand the properties of the Earth's magnetosphere (the Earth's magnetic field) as it relates to how it is influenced by the various forms of radiation emitted by the Sun. ISEE-3 basically wrote the book and invented the term heliophysics. Later the spacecraft was renamed the International Cometary Explorer (ICE) and was the first to visit a comet (Gaicobini-Zinner on Sept 11, 1985), and Halley's comet on March 28th of 1986.
In 2014 this venerable spacecraft returns to Earth's orbit and our primary objective is to regain control of the spacecraft and command its engines to fire on a trajectory that will result in a capture into a permanent Earth orbit. Following this, we hope to return the spacecraft to science operations, using its instruments as they were originally designed. The data from the spacecraft will be open to the public and will be used by the heliophysics community and will be a tool for teaching operations and science data gathering from a spacecraft by students and the public. In the following sections we will detail the engineering objectives of the project until it is in its final Earth orbit.
Engineering Objectives for the Recovery of ISEE-3
Figure 1 shows the trajectory of the ICE/ISEE-3 spacecraft from its last propulsive maneuvers in 1986 until its return to the Earth in 2014:
Figure 1: ICE/IESS-3 Trajectory Through August 10, 2014 (Tick Marks are 14 Day Intervals)
NASA has gotten rid of all of the hardware that understood how to talk to ISEE-3 around 1999. The spacecraft was last commanded in 1986 or 1987. The last time it was listened to, with a carrier only, was in 1999 and 2008. Also, NASA has determined that it does not have the funding to recover the spacecraft and thus on April 12, 2014 the ISEE-3 Reboot Project was born.
Engineering Questions to Be Answered
The principal questions that have to be answered in order to successfully place the spacecraft into a stable Earth orbit and return to science operations are:
1. Is the spacecraft still operational in the same state as for the previous reception by the NASA Deep Space Network (DSN) in 2008 and can we receive signals without the support of the DSN?
2. If the spacecraft is still operational can the equipment and software required to command the spacecraft and read its telemetry be reconstituted on a rapid basis?
3. If the answer to (2) is positive, are there non DSN assets that can be used to command the spacecraft?
4. if the answer to (2) and (3) are positive, can the spacecraft be commanded back into telemetry mode in order to debug the telemetry software system, and determine the health of the spacecraft for a thruster firing?
5. If the answer to (2,3, and 4) are positive, can we obtain an updated ranging to the spacecraft in order to improve on the existing trajectory information.
6. If all of the above are positive, can we reconstitute the programming necessary to fire the thrusters to modify the spacecraft's trajectory as desired?
7. After the spacecraft is placed into a stable Earth orbit, can we return it to science operations.
In the questions above, there are a plethora of subquestions within each one. This is a summary document explaining where we are currently at in the process and to provide an abbreviated path to answering the questions posed above.
Spacecraft Operational Status (Question 1)
We have multiple reception reports from various telescopes around the world. These include Arecibo, the Bochum radio observatory in Germany (AMSAT-DL), the big dish at Morehead State University Space Science Center (MSU-SSC) in Kentucky, and the SETI Allen Array telescope in California. Both transponders have been received and a cursory analysis of the carrier signals indicate that the spacecraft is still in a stable spinning mode with a rotation rate of 18.6 RPM, close to its last known values. Thus question 1 has been answered in the affirmative. The ISEE-3 reboot team now includes the above dishes, with the exception of the Allen array. We expect to add more dishes in the following week. Thus we can consider this question answered in the affirmative
Equipment and Software to Talk to the Spacecraft and Do We Have the Assets to Do So? (Question's 2 and 3)
Since we only started this on April 12th of this year, designing a hardware modulator/demodulator was out of the question. In an extremely fortunate happenstance, Ettus Research has its office less than three miles from ours, and they are experts in the design of software radio systems. Beyond this, the engineers at Ettus think that this is a cool project and they have developed, based upon information that we have obtained from public sources, the modulator that will allow us to talk to the spacecraft. Additionally, the demodulator is under development now and will be available very soon. We are reconstructing this from the documents that we have available. However, soon we hope to have other documents from NASA that will possibly help to clarify things further so that we don't make any mistakes. We have ordered the hardware for four of these Software Defined Radios (SDR's) and should have them in our possession before the 15th of this month from National Instruments, of Austin Texas, the company that owns Ettus Research. Thus the answer to this question is that it is in an advanced state of progress.
We have been able to obtain the most current list of command codes and most of the information that we need for reconstructing the telemetry system for ISEE-3. We obtained these from sources other than NASA. Our internal team has converted the command lists and we have an internal and an external team developing the program to process the command codes. This is obviously the most important part of the system and it will interface with the modulator/demodulator combination.
We are also diligently reading all of the telemetry documentation that we have been able to obtain from public sources. We are going to develop telemetry screens for mission operations for the propulsion, the attitude determination and control system, and the power system. Right now we have a team of experts in Labview, the graphical instrumentation software from National Instruments, developing these screens. We will integrate our data regarding the calibrations, constants, variables, and other outputs from the spacecraft with the Labview telemetry display system. The Ettus SDR system interfaces directly with Labview so we are able to develop this entire system in a fraction of the time otherwise needed. So the answer is that we are moving forward toward integrating the work of several people, spread around the country, in the next week.
As of May 4th, we have three ground stations in our network. The first and most important in the near term is the 305 meter in diameter big dish at Arecibo. This is the largest radio dish in the world and the team down there, led by Mark Nolan, has graciously agreed to provide support to the project on a non interference basis.
The second ground station, and that we will be working with over the next few months, is the dish at the Morehead State University Science center. This 21 meter dish is not large enough to contact the spacecraft now, but will be able to after the spacecraft gets within about 2-3 million kilometers distance.
Our third core ground station is at the Bochum Radio Observatory, and is operated in concert with the Amateur Radio Satellite Organization Germany (AMSAT-DL). We are still working the numbers required to be able to do ranging as well as receiving telemetry at this station.
We are working now with another organization that will be named should our negotiations be successful that is an educational institution that has control over some very impressive dishes. If this works, this may be our prime ground station in California. So this is an ongoing process.
Key to being able to command the spacecraft is the ability to transmit to it on the appropriate frequency. We have two efforts ongoing at this time in this area. The first is that we have a transmitter under construction now, from Dirk Fischer Elektronik in Germany. Dirk is an expert in the design, development, and construction of microwave systems. Microwave is still a black art and Dirk's products are used around the world in the amateur radio community. This transmitter is being provided to the Arecibo telescope facility expressly for the purpose. We expect it to be delivered to the telescope sometime around May 18th. This transmitter will be used, in concert with the Ettus SDR and Labview to attempt to command and receive telemetry from the spacecraft. If time permits we will have Dirk built at least one more transmitter for the folks at AMSAT-DL and for California, depending on several factors still in the air...
We have another transmitter that is under construction that would be sent to Morehead State University Space Science Center. When I get permission I will release that company's name. We will get a shipping date for this transmitter this week. This system will be a loaner from the company and will be used to command the spacecraft after it gets closer to the Earth. More on this as it evolves. So the answer to question 2 and 3 above is that everything is in progress! We have had a lot of success, driven by a lot of volunteers that have shown up that we will properly acknowledge in our next post about our team. It is amazing to behold and if things work as they seem to be, we will fly to Arecibo around the 17th-18th of this month to attempt to command ISEE-3.
Commanding the Spacecraft (Question 4)
There is one prequel to commanding ISEE-3/ICE that we want to do before we attempt to command it. We are going to send a tone to the ranging transponder. We know the transmitter is operational. We want to see if the receiver for the ranging transponder is turned on, and if we can get a return of that audio tone. If that happens, this means that we can range to the spacecraft before commanding it. This may change our sequence of events dramatically as we really would like to do ranging to update the spacecraft's trajectory. (meaning the question 5 may be answered first, before 4)
The next thing we will do is to attempt to command the spacecraft to turn on its engineering telemetry mode. We can determine that this happens by watching the high resolution spectrum from the engineering telemetry transmitter. We then feed that signal into the SDR demodulator to see if we can get bits out. If we get bits out, we feed them to the Labview/Matlab application that will take the bits produced and route them to the appropriate screens. This is the big test and we have two things that we have to debug at once.
The first thing to debut is the demodulator itself. This is done by reading out the bits and see if they make sense in terms of packet size, format, and content. If that works, then we have to debug the telemetry screens to makes sure that for each sensor in each subsystem (power, propulsion, and attitude system) is in the range that it is supposed to be. The difficult part will be debugging the Labview code, our calibrations, and the determining that the spacecraft is functioning properly. This may take a bit of time!! Which is something we don't have by the way. We have experts in Labview working with us and our internal team is handling the telemetry and command formatting so they are giving it their undivided attention.
When all of the above turns out ok we go to the next step.
Ranging (Question 5)
Ranging, without the Deep Space Network is an incredibly difficult affair. We have some ideas on this but they are still under development. Thus, it is pre mature to discuss. At the end of the day, this is our most challenging question to answer. However, we have a few ideas that we are mulling around and should have at least a direction toward an answer by the end of this week.
The ICEMAN Cometh (Question 6)
There is a program that was originally used by the command team for ISEE-3/ICE called ICEMAN. This program was used to implement firing sequences for the spacecraft's thrusters. ISEE-3/ICE has three sets of thrusters, two sets of which we will use to modify the trajectory of the spacecraft to put it on a more optimal path into Earth orbit. Figure 2 shows the spacecraft with its thrusters:
Figure 2: The ISEE-3 Spacecraft Details
There are two sets of radial and axial thrusters in addition to the spin/despin thrusters. The spacecraft is spinning about the centerline that points toward the north ecliptic pole. The spacecraft is spinning at 18.6 RPM which is a little slower than once every three seconds. So what has to happen is that if you are going to thrust in, or against the direction of travel, you have to fire the radial thrusters in pulses. These pulses are timed by a sun sensor that is also mounted on the spacecraft. It is actually a very clever design. Since the thruster is not firing exactly in the direction of travel (since it is spinning), that has to be taken into account as well.
ICEMAN took care of all of these variables. However, it is in fortran code that we, as of this date, don't have. So, what we are doing is going back to first principles and rebuilding the functionality of ICEMAN in Matlab (well Marco Colleluori, our grad student from San Jose State is doing this). We do have some support from some of the former flight team and we may get a copy of the original code. The reason that this is important is that we have found that the thrusters can only be fired a certain number of times before overheating and thus we have to take that into account. We are working to get the code from some of the retirees or from NASA. We will be able to take the output of ICEMAN and feed it into Systems Tool Kit (formerly Satellite Tool Kit) astrogator, where Mike Loucks will simulate the thruster firings from the ICEMAN output to verify.
After the telemetry system is up and running and we know the state of the propulsion system we may try a couple of test firings before we go for the long sequence. At the time when we think we can actually do this, sometime in June, it will take thousands of firing pulses to get the orbit trajectory that we want accomplished so a couple of test firings first is prudent. If that works then we load the entire sequence, and pray. Our objective of course is to modify the trajectory such as to capture into Earth orbit, not the final orbit, but a transition orbit whereby we can then see what we have to do for the final maneuvers. Figure 3 is our graph of panic, which tells us by what date this has to be done before the spacecraft no longer has sufficient fuel for the maneuver:
Figure 3: dV required for Earth Capture Course Correction
When the number on the left goes higher than about 150, it is game over. Thus if at all possible we are going to try and get this done by early June.
Earth Orbit and Science Operations (Question 7)
Due to the press of time and lack of resources, we have not given much thought as of yet to the science instruments. If we get the burn done in June we will have time to work the science instrument issue before the August 10 flyby maneuver. We have a critical issue for the flyby which is to turn on all the spacecraft's heaters for its propulsion system so that it does not freeze during a 25 minute eclipse period during the flyby. The battery on the spacecraft has been dead since 1981 so there is no help there. Fortunately, this spacecraft does not have a computer! The memory on board is not really memory as we understand it today so it will retain and regain its pre eclipse state after it comes back out of eclipse and power is generated by its solar cells.
We are still discussing the final orbit of the spacecraft in Earth orbit and this will be the subject of a future post. By the time we get back into Earth orbit we will have put together the commissioning plan for the experiments. Several of the original principle investigators are either already working with us or have indicated an interest in doing so. It is our strong desire for a mentor relationship here with students to teach them about solar physics, the solar cycle, and the Earth's magnetic field. This is an important field of science that impacts our lives every day. We take a lot of the science for granted that NASA, ESA, and other space agencies do in this area, but without them and the missions that have come after ISEE-3, we would have more difficulty in executing a modern civilization.
Soon we will do a short write up on the scientific objectives of the project.
As I think you the reader can see, there is a heck of a lot going on, and not much time to get it done. Thus, we are going to focus on getting the job done with a minimum of distractions and all but the most essential paperwork. In a very short time, with the volunteers that have come forth, the corporate support we have gained, and the amazing outpouring of financial support in the crowd funding (yes we need every penny of the $125k to do this!), it is starting to look like we have a good shot of pulling this off. The critical dates are in the third week of this month the transmitter is delivered and when we travel to Arecibo where we will attempt the first command session. Please continue to help us reach our financial goal for the project. We now have a really cool patch, designed by our incredible artist, Mark Maxwell. The same for the images that are in our mission prints goodies now. From being a completely insanely impossible thing to do on this short of a schedule, it is now merely insane. Onward Sancho!