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A nano-satellite that lets you take Earth images and "tweet" from space, then inflates a visible balloon, and de-orbits cleanly. Read more

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This project was successfully funded on September 12, 2012.

A nano-satellite that lets you take Earth images and "tweet" from space, then inflates a visible balloon, and de-orbits cleanly.

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Looking Back, Looking Forward

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This is the final update to the SkyCube project. I'd like to begin by thanking everyone who's followed and supported SkyCube over the past 2 years.  You made possible some amazing accomplishments.  You proved that an amateur team can build, manifest, and orbit a functioning spacecraft on a shoestring budget.  You were pioneers in a DIY space movement that - over the past few years - has blossomed into a multi-million-dollar industry.

FINAL MISSION STATUS

At this point, SkyCube's 90-day mission is now complete. Our definitive contacts with SkyCube on March 27th were our last communications with the satellite. Since then, we tried many different command sequences to cut the solar panel restraints, reboot the satellite, and inflate its balloon. These did not generate any apparent response. On July 8th, we stopped attempting further communication. Our efforts since then have concentrated on determining the cause of these results.

SkyCube deployment from ISS, 28 Feb 2014.  SkyCube is the middle satellite in the "train."
SkyCube deployment from ISS, 28 Feb 2014. SkyCube is the middle satellite in the "train."

Interestingly, of the five CubeSats deployed from ISS on February 28th, SkyCube is the last remaining in orbit. It's expected to stay there several months longer; the other four CubeSats in our deployment have all decayed and reentered Earth's atmosphere. We feel this is conclusive proof that SkyCube's solar panels did not open on day 1. If they had, the SkyCube would have had more surface area than any other satellite in the deployment, hence the most drag, and fastest orbit decay.

CubeSats in SkyCube's deployment
CubeSats in SkyCube's deployment

A solar panel non-deployment would explain our other communication problems. SkyCube's radio antennas were tucked inside the solar panels for launch. They could not have extended if the solar panels never released. Antennas folded inside solar panels would explain why SkyCube's transmissions were so weak and sporadic. On March 30th, we tested radio communication with SkyCube's twin in packed configuration, and found that its signal was weakened by about the same amount (10 - 12 dB) as the difference between the expected and observed signal strength in the packets that were actually received on March 27th.

Solar panel non-deployment would also explain why the balloon did not inflate: the tie lines restraining the solar panels were deliberately reinforced, to prevent the lid from opening in case of premature balloon inflation. If the tie lines were not cut loose, the balloon could not have punched through the lid.

SkyCube in packed configuration.
SkyCube in packed configuration.

ONE MYSTERY REMAINS

Our final remaining unanswered question is this: the solar panel deployment mechanism was tested repeatedly on the ground, so why did it fail in space? None of the proposed theories are very satisfying:

  • Burnwires cut nylon more slowly in vaccuum.  We didn't test the solar panel deployment in a vacuum chamber before launch.  But we did test the (identical) balloon inflator burnwire mechanism in vaccuum before launch, and re-tested the burnwire mechanism in vacuum in March 2014.  These tests showed burnwires cutting nylon in 3 - 5 seconds, with no noticeable difference between the time to cut them in air.
  • Battery charge was not sufficient to power the burn wires.  In testing, we learned that a battery charge below 7.25 volts was not sufficient to power the burn wires.  But we programmed the satellite to wait until battery charge was above this level before attempting the deployment.  When signal was actually receieved from the satellite, the battery voltage was over 8V.
  • Burnwires broke due to vibration on launch.  If burnwires came loose or disconnected, applying current would have no effect.  However, burnwires survived all pre-launch vibration tests without incident; and all 4 burnwires would have to have broken in this way.
  • Burnwires worked perfectly, but hinges were mechanically stuck.  Again, we did not observe this in testing, and all four independent solar panels would have to have gotten stuck the same way to explain a complete failure.

The truth is that we may never know the answer. Rather, we view this as a lesson learned: if this is your first satellite, design it without moving parts that are required to deploy for mission success.

WHAT WE ACCOMPLISHED

Given the solar panel deployment problem, it's even more remarkable that we did actually hear from our satellite on orbit. The contacts on March 27th proved that the satellite's electronics had been working normally for at least a month. The batteries were fully charged; the solar cells and power system worked as designed.

This also means that all of your names were actually transmitted by the satellite as "tweets" (albeit quietly, through folded antennas) during the mission's first week. Those tweets are still streaming out across the universe on 915 MHz at the speed of light.

Our ground station operators at Saber Astro and elsewhere also deserve special mention. During the difficult post-deployment period, after the first suggestive transmissions were received, they patiently kept listening while 3 weeks of silence followed. Through the silence, they repeatedly pinged each of the five candidate objects for a response. Without their persistence, that response would have never been caught.

THE BIG PICTURE

Over the 2+ years since this project began, CubeSats have made enormous progress in general. When SkyCube's kickstarter launched in July 2012, they were an academic curiosity. When SkyCube's kickstarter began, the greatest number launched in any year was fifteen (in 2010). So far in 2014, more than sixty CubeSats have been launched. On our own launch, 33 CubeSates were carried into orbit. Of those, 28 were commercial earth-imaging satellites, operated by Planet Labs in San Francisco. In July, NanoSatisfi - whose ArduSat kickstarter preceded ours - announced its transformation into Spire, a global asset-tracking service using CubeSats. The same month, Spaceflight Services announced a new commercial small satellite communication service.

Movement really is happening. Significant venture capital is flowing into the field. Communication challenges are being addressed. Access to space really is getting easier. Our timing may have been a bit eariy. Our results may have been different if we'd started now instead of 2 years ago. We were pioneers in the movement, and performed a tremendous amount of work on an incredibly small budget. Hearing from SkyCube on orbit - at all! - was a more successful result than the majority of first-time CubeSats achieve. And we have a lot of very hard working and talented people to thank for that.

Finally, we have all of you to thank. Although this particular chapter may be closing, the larger story of the New Space movement is far from over. We encourage you to take advantage of our lessons learned, to take on new challenges of your own, and to view what we all accomplished not as falling short of some specific goals, but as a groundbreaking achievement in the democratization of space exploration.

You have our gratitude for making it possible.

-Tim on behalf of Team SkyCube

The Bottom Line

24 likes

Hello, team SkyCube!

We presented our results so far at the Cal Poly CubeSat workshop last week. More on that below - but first, a mission update.

We've continued to send "deploy solar panels" commands to SkyCube from all ground stations when the satellite is passing over them. We've not yet gotten confirmation that this strategy has worked. One ground station is enhancing capabilities with a new 3-meter dish, and Saber Astro is installing new noise-reduction circuits. Though we're still awaiting results from those efforts, we remain hopeful because the communication we've had to date indicates that the electronics and power system are healthy.

Lessons from Cal Poly

At the Cal Poly workshop, it's became apparent that our experience is not unique. For example, of the 28 CubeSats deployed from last November's ORS-3 launch, half were never heard from in space, and at this point only 4 are still transmitting. One came back after a "winter vacation" where it went silent for 2-1/2 months!

CubeSat communication has proven to be more challenging than any of us expected when this project began 2 years ago. There isn't any global standard - rather a patchwork of different amateur and university programs that collaborate to varying degrees. For amateur CubeSats projects to succeed more frequently than they do now, this situation will have to change.

The Bottom Line

Our presentation at CubeSat was about the fiscal, rather than technical, challenges of running a CubeSat mission. Here's a picture that sums it up:

SkyCube total program costs to date
SkyCube total program costs to date

Hardware is only a small part of the total. Software, operations, and communications - i.e. the human expenses - far outweighed them, and are just as critical to the mission as the launch itself

We built two satellites. It make sense to orbit another after we fully understand, and can correct the problems with the first. And when we can fund it. The way forward with our space program - just as NASA's - will be determined by fiscal inputs as well as technical.

That's the most accurate picture I can give you at this time.

-Tim

We Have Identified SkyCube

80 likes

I didn't expect to write this update.

For most of the past 3 weeks, there had been no definitive contact with SkyCube from any ground station. Although some 915 MHz signals were heard when a candidate object passed overhead, none of them were conclusive. We've been unsure which of the 5 objects released from ISS on Feb 28th is really SkyCube, and all information provided to us by other teams indicated that the official designation of 39569 = SkyCube is wrong.

On March 14th, a Russian amateur radio operator (Dmitry Pashkov, UB4UAD) reported a 915 Mhz signal which looked suspiciously like a SkyCube telemetry tweet. But the signal was not decoded, and the date/time it was received, plus the direction which his antenna was pointing, indicated that the signal came from the wrong satellite (specifically, 39569, identified as LithuanicaSAT-1).

On Friday, March 14th, we used the 60-foot radio dish at Stanford University to attempt contact. No response was received. We had been preparing to declare the satellite lost.

Back from the Dead

This all changed last night. While reviewing our server logs, we discovered that the Central California ground station had recorded a response from SkyCube on 27 March 2014 at 07:52:47 UTC. At that time, the station was pointed at object 39567, at an elevation angle of about 33 degrees and a range of 700 km.

The ground station received a 915 MHz signal, which was was digitized, decoded, and passed to our server along a secure SSL connection. It was an encrypted 16-byte sequence. Our server decrypted the sequence to the following meaning:

Battery voltage = 8250 mV
Solar panel current = 0, 0, 0, 1, 0 mA
Date/Time = 2014/01/27 14:55:15
System uptime = 2301542.12 seconds
Processor temperature = 16.7 degrees C

Here's what this means: the battery was near fully charged. The solar panel current readings, all near zero milliamps, make sense because the satellite was passing over the ground station at night. The low processor temperature is consistent with this - we see temperatures of 25 - 40 C when testing our satellite in sunlight.

SkyCube is programmed to think it's midnight, January 1st, 2014 when it first powers on. If this happened when SkyCube deployed on 28 Feb 2014 at 07:30 GMT, then it would think the current date is Jan 27th when the transmission was received on March 27th. (We never sent it a SET_TIME command to tell it the correct date.) The system uptime of 230154 seconds means that the processor has been running continuously for 26.7 days.

This data packet came over an SSL-secured connection from the IP address of the Central California ground station. To get passed to our server, its first 8 bytes had to be correct. The packet decrypted and passed CRC validation. The decoded data was sensible. There's just no way this could be anything but a response from the real SkyCube in orbit.

Why now? What's next?

SkyCube is still alive, in space, and has been operating for at least 27 days. And we know know, definitively, that it's NORAD object 39567. But why are we only hearing from it now?

Partly, it's because we've spent a lot of time listening to the wrong objects. Until now we could not prove which one was ours. And we now also suspect that only one or two of SkyCube's solar panels deployed on day 1. That would explain why so many initial contact attempts failed. Only one or two radio antennas were exposed, and the satellite had to be facing just the right way to pick up a signal from the ground.

Right now, we're sending commands to release the solar panels. Those may or may not work. If the solar panels & radio antennas remain stuck, then occasional, sporadic broadcasts may be all we ever get. But this is still a huge improvement from where things stood 24 hours ago. We now know definitively which satellite is ours, and where it's located at all times. We know that it's been operating for many weeks and survived hundreds of orbits. We know that the ground stations and server infrastructure designed to talk with SkyCube's C2 radio on orbit can actually do so; this had not been proven before.

And we also now know that an amateur team can build, manifest, and orbit a satellite that functions in space, on a shoestring budget funded by volunteers around the world, a few dollars at a time. No matter what happens next, that's groundbreaking history that you helped create, and you should all feel proud to be a part of it.

Thanks for making it happen.

-Tim, Rouslan, Scott, Kevin, Mark, and the rest of Team SkyCube

Searching for SkyCube

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Nine days ago, five objects were released from the ISS. NORAD assigned them tracking numbers 39567 thru 39571. One of them is certainly SkyCube, and it's the only one that transmits on 915 Mhz. We detected a clear 915 MHz signal near ISS the morning after SkyCube deployed, and a second time on an iSS pass over a different ground station later that afternoon.

 Since then, those objects have drifted hundreds of miles apart, and thousands of miles from ISS. Each ground station can really only track one object at a time - unless they're close enough to fit into the station's antenna beam. And then you don't know which one you've detected.

Twice last week, a 915 MHz signal was detected by two different ground stations (Australia on 3 March at 10:46 UTC; California on 4 March at 21:57 UTC). Both signals came at times when 39570 was passing over the ground stations that detected them. That's suggestive, but not conclusive.

On Wednesday, NASA, Celestrak.com - and Satellite Safari - assigned identifications to objects 39567 - 71 in the order they were released from the ISS. Those identifications are surely wrong. The satellites swapped order since their release; they have different masses and sizes, so atmospheric drag affects them differently. On some passes, we may have been trying to communicate with the wrong object(s).

So how do we tell who is who? We've been in contact with the chief engineer of Lithuania's satellites, LitSAT-1 and LithuanicaSAT, deployed at the same time as SkyCube. Laurynas writes:

"We noticed NORAD associated numbers to the satellites according to the order they were released from the NanoRacks deployer. This is of course not accurate since sats have taken other positions in orbit. For Your notice, it seems that two Lithuanian birds have received good TLE references from german ham radio operator Mike Ruprecht, see his webpage. We are now almost continuously tracking our LituanicaSAT-1 with NORAD catalouge no 39568U with good results."

Mike Rupprecht's identifications are: LITSAT-1 = 39568, LITUANICA = 39569, UAPSAT = 39571. These identifications disagree with NASA's. At this point both may still be wrong.

The process is like trying to figure out who's who in a group of gnats flying around inside a football stadium, by listening to each gnat hum a different tune, for a few minutes each day. It's going to take a while to sort them out.

In the meantime

Many of you are amateur radio operators who've asked for information to help track SkyCube's beaconing signals. Here's what SkyCube should be doing:

Every 3 minutes, SkyCube broadcasts its telemetry at 915 MHz with BPSK modulation at 9600 baud. The data is in a single AX.25 packet containing human-readable ASCII text, prefixed and followed by 2 seconds of preamble. The entire telemetry "tweet" should last about 4 seconds, and repeat every 3 minutes.

Today, we are releasing the first public beta of Scott Cutler's SeeDeR software. It's a Windows program that can decode AX.25 radio transmissions using inexpensive USB software defined radio (SDR) devices. You can also download a pre-recorded sample of a SkyCube "telemetry tweet". This is what to listen for.

SeeDeR playing back pre-recorded SkyCube "telemetry tweet"
SeeDeR playing back pre-recorded SkyCube "telemetry tweet"

Finally, many of you are amateur astronomers. As Sky & Telescope mentioned, experienced satellite observers may be able to image the CubeSats with a CCD camera or even visually, with a large (16"+) backyard telescope and dark skies.

Please report any radio or optical detections to skycube@southernstars.com. Please include the date/time of your observations, your observing location, and equipment used. Please include any images, SDR recordings, screenshots of waterfall diagrams, etc.

We'll continue efforts to locate SkyCube and establish communication this week. Patience and persistence are the name of the game. This is just the beginning.

-Tim, Scott, Rouslan, Mark, and the rest of team SkyCube

SkyCube Is Alive

56 likes

All-

SkyCube deployed from the International Space Station last night, at 07:30 GMT -  half an hour before midnight here in California.  These three videos show three different views of the deployment.  They were provided by Nanoracks, courtesy of NASA:

After that, ISS and SkyCube passed into Earth's shadow.  There was a 45 minute wait before the solar panels & radio antennas could deploy. SkyCube had been in cold/dark storage for 4 months, we never tested how the batteries hold charge over that long; they may have discharged; it may take several orbits to recharge up enough to fire up the burnwires that release the solar panels. We just did not know.

This morning, the satellite just made its first North American pass, over New Mexico. We repeatedly sent it "Get telemetry" commands, meaning "send me your battery level, solar panel voltages, overall health level, etc."  For the first minute or two, no response. Then the ground radio started detecting signal at the expected 915 MHz frequency, then a digital signal at the right baud rate. It wasn't quite strong enough to fully decode all the bits, but there was definitely signal coming back. The signal stopped coming back when the satellite crossed over the horizon, as expected. The guys here are sure that was signal from the satellite.

If they're right, this means that the solar panels must have deployed some time last night, and released the radio antennas. And the processor board is working. And the batteries didn't die after 4 months in cold storage.

The patient is alive. Stay tuned.

-Tim