How clever mechanical design was the key to getting CARBONITE-1 into orbit.
A couple of years ago the space industry saw a shift in the downstream market for space data with new start-ups attracting investment for novel space-based applications and many of these new applications will require daily-revisit earth observation data from constellations of low-cost, rapid-build, satellites to close their business case.
A launch opportunity requiring a bespoke deployment mechanism
With this in mind, in 2014 we began developing plans for a new low-cost, rapid-build micro-satellite technology demonstrator that would carry a Commercial-Off-The-Shelf (COTS) telescope and HD video to orbit. We called the new micro-satellite platform CARBONITE-1, and as the platform designs began to come together we identified an ideal opportunity to launch CARBONITE-1 together with our three DMC3/TripleSat satellites on board ISRO’s PSLV-XL launch vehicle. We were immediately in “All systems go” mode with just 6 months to complete the build and 2 major challenges to overcome: we had to build the new microsatellite with very tight size and weight constraints in order to use the limited available space below a large deck on the rocket, and we had to design a completely new deployment mechanism that would eject the spacecraft sideways (instead of the usual “release-and-slide” mechanism), to prevent it from hitting the upper deck of the launch adaptor.
|Graphic showing CARBONITE-1 mounted on the PSLV-XL rocket, and the approximate side-eject angle required for safe delivery into orbit
At SSTL we are very used to working with complex size and weight constraints for our customers, so the platform design itself was a fairly routine engineering challenge – however designing a new deployment mechanism from scratch in a 12 week timeframe was a big challenge, but one our engineers relished!
Once we had made the decision to go all-out to take up this launch opportunity for CARBONITE-1, we quickly assembled a team of engineers to work on the new launch deployment mechanism that would be required, and they set to work. The basic concept of the new deployment mechanism uses spring loaded lever arms of different lengths to impose an angular motion, with a set of rollers on the side of the rocket engaging with C-sections on the spacecraft. The design includes micro-switches, links guides, and stops which act together to prevent movement in the axial direction with respect to the launch axis, prevent premature release during motion, and to define the rotational speed of the spacecraft as it leaves the rocket.
As the project progressed, the engineers identified additional challenges. Due to the low rotation rates of the spacecraft at the point of ejection, and the physical position of equipment around the separation panel, work had to be done to eliminate any potential clashes between the spacecraft, the separation ring and panel, and the side of the rocket. We used 2D analysis to size the link lengths, check the C-section geometry, release angles and torques of the springs and achieved a theoretical successful separation of the spacecraft. We then undertook sensitivity analysis to demonstrate that, even with different torque values, successful separation was still achieved.
The test campaign
Theory complete, the engineers built the new deployment mechanism with majority COTS components to keep costs down and for a rapid build schedule. Our first test campaign was to vibrate the new deployment mechanism attached to the spacecraft to check that all the mechanics and components would hold intact during the rigors of a launch. Next the mechanism underwent thermal cycling and finally we were ready to move on to the most exciting, but nerve-wracking test - simulating, as accurately as possible, the process of firing the spacecraft off from a rocket.
For this next phase of testing we attached the deployment mechanism to an old separation ring, using a clear plastic separation panel to allow us to view the link arms in action. To this rigged up separation and deployment assembly, we suspended a mass dummy representing the CARBONITE-1 spacecraft using 4 long strops attached via a horizontal lifting frame to a single cable over 10m high suspended from one of our overhead cleanroom cranes. A laser and a Go-Pro camera were mounted on the front of the mass dummy, projecting onto a grid laid out on the floor of the cleanroom so that a video of the laser movement profile could be mapped for later co-ordination with the analysis.
Numerous deployment tests were performed and all were successful, allowing us to replace the mass dummy with the real CARBONITE-1 spacecraft, and again we were very relieved and pleased that all the deployment tests went smoothly and to plan.
Launch authority sign-off
The new deployment mechanism design and test results were presented to our colleagues at ISRO/Antrix, the launch agency, and were passed for launch authority sign-off. We were all systems go for launch.
Success! Textbook side-ejection achieved!
On 10th July 2015, CARBONITE-1 was successfully ejected from the PSLV-XL rocket, to begin its mission lifetime in orbit. Initial data from the magnetometers on board the satellite recorded a day after launch showed that spin rates were up to around 15 degrees / second max around any axis, which was a very acceptable result.
CARBONITE-1 is operational in orbit, and is delivering images and video, proving the COTS technologies on board for future missions.
Future CARBONITE and nanosatellite missions are in the pipeline at SSTL, so we may need our side-ejecting deployment mechanism again in the future – or a variant – and if we do, we’ll be ready to meet the challenge.