In addition, about 120 young engineers from 25 countries started their career on our premises, often with unique hands-on work. With this background in their pocket, they went off to make their way into the space world. Hundreds more around the world worked on our inspiring projects remotely. Delta-Utec has thus been a real, European incubator for space ideas and initiatives.

TeamSat, the YES1 and YES2 satellites; the Fotino and inflatable re-entry capsules; the tether deployment test facilities and a record-breaking 32 km deployment in space; the SSATT star sensor tool, the ALBATROS tool, the discovery and exact location of the Peaks of Eternal Light on the Moon: they are some of the notable achievements of our company. The TeamSat/YES1 success lead to co-located ESA projects such as EuroMoon and the set-up of the successful Concurrent Design Facility at ESTEC. They were also an inspiration for the SSETI project that lead to the SSETI Express student satellite.

Our goal has always been to show that with not much more than persistence and dedication, you can make your dreams alive. Together with our highly motivated employees, Erik and I have demonstrated this. Various enthusiastic employees have now started their own innovative companies: a new generation has taken the initiative. We think it is time to make room for their dreams.

We hope that tether technology will continue to move forward. Michiel is completing his PhD on this topic and will continue his career at ESTEC in a different field : Integrated Applications Promotion. Erik is involved in ACS development at Bradford Engineering, always a supporter of YES2 and our tether technology developments. A new SpaceMail experiment is in the planning and there are many roads that lead forward. Delta-Utec will close per 1 September 2009 (over 14 years after we conjured up the acronym : DUtch TEther Company), but its legacy lives on!

Tension test set-up.

Typical tension development as the tether unwinds from the criss-cross spool. The level at the Top of the spool is an indication for stickiness. The Up level provides an idea of the stiffness and settling effect. The peaks of the layer crossing passes indicate the "hooking" effect of the tether bent around the layer transitions. The Down level is the highest level, because the tether has to jump a layer as it is pulled off the spool and travels towards the top. The increase with respect to the Up is another indication of shape memory and hooking effects.

The tension signature as a function of test condition and depth into the spool (from left to right about 3 mm).

The fresh wound tether has low unwinding tension (1,2). Thermal changes cause a settling, memory and hooking effect (4,5). Different subsequent test conditions have little further influence (7,8,9,10,12,13), suggesting that chemical/mechanical changes in the tether finish and maybe also exposure to humidity contribute not so much. After a break, the tether relaxes over a lenght of about 15 m resulting in lower unwinding tension (3,6,11). Vacuum seems to reduce tension a bit (7 vs. 5), but deeper in the spool the tension grows again to the prevacuum condition (14), possibly due to reduced outgassing at increased depth. Another, less trivial, explanation of the results could be that humidity needs many days to penetrate the spool and has a lubrication effect at room temperature, but increases tension at low temperatures.

As described in my previous message, the YES2 legacy continues. A 5 km tether has been wound for an experiment on Progress around 2011 (Baumann institute in Moscow). We are also started a YES2 reflight preparatory study on a Shtil (with Makeev) or perhaps Bion (in co-operation with SSAU). The Acta Actronautica paper with first mission results will be published very soon. The Aerospace America featured a nice summary of the YES2 mission data analysis in its overview of defining moments of 2008 (with a picture of Dimitris working on the satellite).  We have in the mean time also rebuilt the YES2 electronics system and we could reproduce similar behavior as seen in flight, which means that we have identified the likely cause of the failure of OLD electronics  that stopped the deployment control some 2300 s before deployment completed (brace yourself for some technical detail).

Test set-up reproducing flight results. R1 simulates the internal short (15 Ohm) in one of the OBC's interrupt line. This short was present before flight and the signal was made functional by a patch (the transistor) that consumed a too much power for the small DC/DC converter, putting noise on the other RS422 receivers that are meant to feed OLD signals to the OBC.

What seems to have happened  is the following: as both the flight and spare YES2 (commercial) on-board computers showed some anomalies before flight, an electronic patch was added to the flight board as an ad-hoc solution. This patch required a 5V power supply. YES2 had available two 5V power supplies, a small one (1.5W) for the most critical circuits such as pyro firing control and telecommand handling, and a large one (30W) for deployment control and secondary functions. It was decided, for consistency, that the patch was to be powered from the small supply for critical functions. This proved to be a mistake. The patch demanded significant power, and the 1.5W power supply was used close to its maximum limit, increasing noise levels and decreasing voltage. As the temperature of the system increased during the mission by various degrees (in itself fully nominal), the sensitivity of the on-board computer signal input lines to these parameters increased, until the point that the noise itself was generating interrupt signals, at as high as 10 kHz, swamping the actual deployment data. The software filter (correctly) identified the signals on the affected channels as false and rejected all of the interrupts arriving from them (including the swamped good data). As a result, the measurement of length increments effectively stopped at this point. The controller assumed then that deployment had stopped and reduced the brake force. This lead to accelerated overdeployment and an abrupt stop of deployment when the tether was fully deployed. It is unfortunate that this problem could have been easily avoided. The reason that this was not down boils down to the time pressure and the fact that the team at the time the patch was installed (shortly before satellite delivery) was overworked. The budget for building and testing YES2 was released only 9 months before delivery, which put tremendous pressure on the team. Tests were nevertheless performed after installation of the patch to demonstrate good performance, but these tests were done in ambient conditions and did not feature the rise in temperature that was seen in the mission. Alternative ways of preventing the failure would have been: earlier budget release/start of integration test phase to buy time for fundamental solutions, replacing the on-board computer rather than patching it (not possible due to lead time), powering the patch from the 30W supply (simple and effective),  accepting the anomaly (even simpler and ok as the affected function was covered by redundancy), inverting the input signal to the patch (reducing the power consumption greatly with little effect on performance).

Analysis of the data shows that each one of these actions would have led to a proper deployment control till the very end and a nominal Fotino re-entry with a landing site very close to the location of the recovery team (tens of kilometers).

The research so far suggest other improvements that should be made for a reflight of YES2, that would lead to improved preformance and better chances of Fotino recovery:

- Deployment test after tether exposure to vacuum (this was planned but was eventually dropped because of time problems)

- Pre-flight analysis of controller resonance occurrence and identification of the (simple) remedies, which would have avoided excitation of lateral waves and would have further increased re-entry point precision.

- Monopole antenna on FLOYD rather than large hexagon loop (for better reception of MASS data considering reflections of MLI) 

- Redundant capsule beacon system, with monopole antenna's instead of DDRR (more robust).

We keep you informed!

I find it unbelievable but true. It's been already one year since the YES2 deployment, perhaps the most ambitious student space project ever. Time raced by, as I was studying the data from many many angles. And as it turns out from my analysis performed over the last 12 months, it was a highly successful tether experiment. There are so many sources of complementary and highly detailed  data that analysis will continue for at least one more year. But many essential results have already been obtained, first rough ones early this year, then improved/detailed during the Summer months.

The YES2 students have moved on and can be found working at ESA, in responsible positions at EADS, or with new start-up companies in Poland, Greece and other countries. Our sponsor Emxys is now active and respected member in the Spanish space industry. In SSAU and other universities in Russia research on tethers is continuing, inspired by YES2. Myself I am amending my PhD work on tethers with the YES2 results. Flight data is a great addition to a thesis.

It is probably difficult to understand for an outsider what it means to have been part of YES2. Was it just an industrial project without real education?Or was it the opposite, just a student project? Of course it was neither, but a highly educational project organized in a flexible, industrial manner. Every team member knows he (or she) was part of something very special that will not easily be described or repeated. There was a great atmosphere throughout the project, and a warm feeling of being joined in doing something unique. From the beginning till the end we were surrounded by both supporters and by skeptics. There were incredible challenges - yet eventually they were all overcome.

Critical technologies never available before to European industry were developed to space standards through the continued efforts of the team members. The successful tether deployer system is the most noticeable but certainly not the only result. Each and every subsystem of the three independent YES2 modules, were designed, built and qualified by students as well as many test facilities and most software tools. The documentation that was maintained, allows efficient reproduction. Note that all detailed design work is publicly available. The YES2 approach to Project Lifecycle Management finds interest in industry, universities and ESA itself, e.g. through YES2's generic Albatros PLM tool.

ESA dedicates a special anniversary report to YES2:

http://www.esa.int/esaED/SEMCO5Q4KKF_index_0.html

The data has allowed to demonstrate deployer hardware performance, flight performance of the ejection system, simulation vs. flight data matching, deployment and trajectory reconstruction, Fotino landing capsule trajectory and dynamics, control S/W, electronics, GPS and RF performance. Already 8 complementary conference papers on the data analysis and about 10 more about post-flight simulations and design/testing were published so far this year (4S, AIAA, SPEXP, IAC). 1 Paper is submitted as a special feature in Acta Astronautica, and one for the Journal of Spacecraft and Rockets. Email me for digital copies of the papers.

Although the YES2 tether deployment experiment can be called a success the SpaceMail demonstration unfortunately can not (yet), as the re-entry capsule gave no sign of life after being dropped to the desert between Caspian and Aral Sea. Recovery was not an objective and although the supposed landing site has now been determined no field excursion is planned. Chances are slim that people will come across the capsule by chance in this abandoned area (there are basically no roads), but I am keeping my fingers crossed for a nice surprise one day in the future.

With all the lessons learned Delta-Utec is now developing a set of recommendations for a follow-up mission - this mission is for now simply called SpaceMail, and may be on a dedicated launcher. It would contain essentially the same tether system and mission, a custom launcher interface, slightly adjusted control electronics, and a simplified subsatellite/capsule with improved possibility of recovering the trajectory.

 "The Young Engineers' Satellite 2 (YES2) was launched on board the Foton-M3 microgravity mission on 14 September 2007. On 25 September YES2 unwound an experimental package on a 0.5 mm-thick cable in order to test the principle of returning payloads to Earth without the use of retrorockets. Experimental data show that the cable successfully deployed to its full length of 31.7 km (19.7 miles), the longest manmade structure ever deployed in space." 

Because of many requests, please find the Thank You poster attached.

The program reveals interesting topics from YES2 to Earth observation satellites: www.volgaspace.ru/school.

Prof Belokonov says:"Wellcome for all students. New projects are waiting them."

In the days to follow (2-5 September) there will be a conference in Samara (just keep hanging around). There is a call for papers-deadline May 15th and topics like YES2 and flight opportunities for next Bion missions should interest you: http://volgaspace.ru/SPEXP2008/en/index.html

This colorful picture shows a fit of YES2 rate date (dark blue, loops per second vs. deployment time in the second stage, peaking at 65 Hz at deployment completion), as derived previously, vs. a recent spectrograph from RedShift's DIMAC accelerometers (green, yellow, red). Amazingly, the rattling of the tether (with a mass density of only 0.2 gram per meter) as it unwinds inside FLOYD [those who have been at the deployment tests know the sound of it!] is visible as accelerations on the 7000 kg Foton spacecraft, and shows up as a curve of high intensity in this plot of frequency vs. time . The match of the two independently determined curves provides direct evidence of the correctness of the deployment reconstruction by the YES2 team, as the overlay is near perfect, and confirms once more the full deployment of 31.7 km tether.

From DIMAC also the deployment angle could be determined (with about 5 degrees accuracy), and compared to the YES2 reconstruction. A clear confirmation was obtained from phase and amplitude of the swing during the hold phase (between first and second stage), as well as the angle during most of the second stage. Amazingly, the complex lateral (sideways) waves in the tether during the swing back to the vertical could be resolved as oscillations on the tether angle at Foton, both in DIMAC data as in YES2 simulations of the mission that were meant to match the flight data. The match is uncanning and shows how the YES2 mission data is already providing a yet unseen understanding of tether behavior in space. The data confirms the YES2 reconstruction, namely that the Fotino was released nearly exactly at the vertical, which would have sent it towards the Uzbeki-Kazakhi border (see earlier story on this site).

The fate of Fotino is better understood today. Based on deployment simulations including the MASS/Fotino attitude behavior, matched to DIMAC data, it seems likely that Fotino went through a rather nominal release and re-entry, and there is no reason to believe it would not survive:

- At the end of deployment, the shock was small enough not to induce full rotation of MASS/Fotino so the Fotino was probably not entangled in the tether.

- At the time of Fotino release, the Fotino was properly oriented and tether forces were optimal for separating Fotino effectively from MASS (similar to best case parabolic flight tests)

- At the time of Fotino release, Fotino's angular motion was less than 30 deg/s [See image below]

- In the worst case of a 30 deg/s rotation at atmospheric entry, simulations show that Fotino stabilizes in time at 105 km altitude, and oscillates around the nominal stagnation point by about 50 degrees, which is still within margin. The simulated heat flux is still significantly less than that tested in the plasma chamber. [See image below]

Based on matching of the deployment/re-entry simulation to the YES2 deployment and DIMAC data, the red ellipse in the map provides an indication of the currently suspected Fotino landing area.

Did Fotino land in the Aral Sea? Fotino floats, but could not be made waterproof. It would explain why the beacon signal was never received as it would not survive for the 2 hours required to be picked up by ARGOS. However, Fotino would likely have floated to a shore, so that is where it may be found. Remember, there is a financial reward for those who find it :)

The indicated zone is NOT FINAL, because the simulations have not been completed yet. It is expected the estimate can be significantly improved based on future results. The red zone is for the case of successful or slightly delayed release of Fotino from MASS at the end of the swing. The orange zone includes also the case of release failure. Originally intended landing point (Tasty Taldy) and launch site (Baikonur), as well as the Russian Center of Expertise (Samara) are indicated.

The long awaited DIMAC data sheds new light on YES2 and the workings and influence of the Foton attitude thruster. It is now confirmed that the tether deployment stopped at 8625 s, as suspected earlier. New is that it is now certain that the tether REMAINED attached when deployment completed and a swing back to the vertical was started! At the proper time the tether was cut. It also seems that Fotino was released at the right moment and deorbited into Kazakhstan. Features such as the stepper driver/barberpole activity can be clearly recognized, as well as the hold phase (gravity gradient tension), including longitudinal tether oscillations. During the swing, jerks such as those predicted are visible (see separate article below).

Above picture compares the YES2 measured tension after ejection to that derived from DIMAC Foton accelerometer data. An amazing fit!

The DIMAC data shows a clear tension component that indicates significant deviations (up to 30 degrees) of Foton attitude from the vertical. From this it could be understood what was the Foton attitude control algorithm, which turns out to be quite different from the one expected. The new understanding resolves some apparent contradictions in our earlier analysis (see also below).

The DIMAC data shows accelerations of Foton resulting from disturbing forces. During the YES2 mission, one of the major disturbances is the YES2 tether tension. So in a way, the DIMAC was also a tether tension sensor. The data is high quality and very rich in information for YES2. It will keep us busy for months. A first glance tells us:

• The tether deployment stopped abruptly at 8625 s, as expected. The DIMAC derived tension profile is generally consistent with the 31.7 km best fit deployment case reported in the YES2 data analysis report. Although it must be admitted that presently sensor drift makes it difficult to distinguish between deviations and drift effects (this will be improved in the near future) the swing behavior and bouncing, deployment angle and Foton orbit raising all match the best-fit 31.7 km scenario and together provide a very strong case.
• A large shock (~30 N) followed, higher than expected.
• The tether remained attached to Foton, so the piece of tape at the end did NOT come lose.
• The tether was cut from Foton according to the timeline (9364 s).
• It seems that the release of Fotino can also be confirmed from the data, there is a sharp drop in tension visible some seconds after Fotino release time (9344 s).

This could mean that the entire SpaceMail mission was completed, and Fotino was sent into a trajectory towards Kazakhstan, and must have landed upstream (roughly between Baikonur and the nominal landing point near Astana), case G in the report, possibly towards case J.

We still need to study when exactly Fotino came lose from the belts to determine where in between these cases Fotino ended up.

• The delay between Fotino release time at one end of the tether and tension drop at the Foton end would be valuable information on the speed of sound in the tether, and seems to be consistent with expectations (several kilometers per second).
• The proper performance of the stepper driver and barberpole brake can be confirmed, as the tension signature due to braking is clearly recognizable. This data allows for separating several types of oscillation observed in the tether during the first stage deployment so we can learn about details of deployment dynamics that do not show up in ground tests.
• The tension during hold phase is as expected, and shows oscillations which will tell us about stiffness (EA = 120 N at 0.2 N tension, matching ground measurements) and damping of the tether, allowing us to improve simulations. 
• The bouncing of the tether after deployment (picture on left) matches well the preliminary deployment reconstruction simulation (see insert and image on right), the difference in timing tells us more about the tether stiffness and thus in a next iteration we can better simulate the bounce and learn about the dynamics of Fotino at time of release (was it stable or spinning?).
• The DIMAC measurements shortly after ejection can be overlayed well with the YES2 tensiometer data, and demonstrate the DIMAC data is a good representation of tether tension. (See separate article).
• The tether angle with respect to Foton could be derived from the direction of the acceleration in Foton body frame. Combined with the YES2 deployment reconstruction performed earlier, a detailed coherent picture appears on the Foton attitude during the deployment and swing. See picture below. For the second stage this conclusion was already confirmed to several degrees precision from DIMAC magnetometer data.
• Foton attitude control thrust could be filtered from the data and it was shown that Foton Attitude Control System (ACS) maintained an angle with the vertical of about 30 degrees while the tether climbed to its swing angle. The Foton torque followed well the tether-tension induced torque during this time. See picture below. While the tether was at lower angles, it appears Foton attempted to follow the tether direction, minimizing the control torque requirement.

Potentially critical open issues are still:

• uncertainties due to sensor drift over time, which will be estimated by RedShift at a later stage.
• There is possibly a deviation of about 10 degrees in the hold phase swing angle between RedShift magnetometer data and YES2 deployment reconstruction which may indicate a slightly different first stage deployment from so far assumed. Further work into the first stage deployment reconstruction is necessary.

OTHER NEWS 

Further analysis of earlier ejection data shows that the pitch-off rate measured by the gyro was about 4 degrees per second, and maximum amplitude just after ejection would then be about 30 degrees. This information should allow for improved subsatellite simulations.

(*) It was so far demonstrated that the problem was present in the flight model at time of delivery, but NOT in the engineering model, so it is probably related to an electronical patch that was installed shortly before delivery on the flight model only and tested due to time constraints only till 4 m/s compared to the max. velocity of 13 m/s in YES2 flight. Ilias has performed some breadboard testing suggesting that thermal (heating) effects related to this patch may be to blame, but this is yet unconfirmed. IMTsrl is testing the electrical interface on the OBC board. A test will yet be performed at Delta-Utec to make demonstrate the software was indeed able to deal with the velocity (as it was in the engineering model) so that the problem can be narrowed down to the electrical interface hardware.

Today we received the first results from SSAU GPS data, displaying the altitude as function of time. The yellow vertical lines indicate the important events Ejection, Start Second Stage, Cut Tether, from which can be seen that most of the First Stage and the full Second Stage are covered by the available data. Also post cut data is available to study the new orbit of Foton after tether release. The Hold Phase (just before Second Stage) is covered by a large number of data points, even if there are some holes in the data, it should be sufficient to filter out the exact motion and tether deployment behavior: by detailed analysis of the GPS data and determining deviations of the Foton orbit with respect to the expected motion of the center of mass, the tether dynamics can be derived.

In addition to this important mission result, DIMAC accelerometer data is expected early February.