The European Space Agency (ESA) will test new rendezvous sensors on their next Automated Transfer Vehicle (ATV-5) mission to the International Space Station (ISS). The Laser InfraRed Imaging Sensors (LIRIS) will provide another example of the continuing improvements to the “eyesight” of spacecraft, as they conduct rendezvous and docking operations.
The successful rendezvous and docking of spacecraft travelling thousands of miles per hour remains a challenging prospect for any spacecraft.
In the early days of the space program, several Soviet attempts during the Vostok program failed, as did the initial attempts during the early part of NASA’s Gemini program.
The first successful rendezvous was accomplished by NASA astronaut Wally Schirra in 1965, when he managed to guide his Gemini 6 spacecraft within a foot of Gemini 7.
The two craft did not dock, but given the successful use of orbital mechanics and the close proximity, it was deemed to be a successful rendezvous.
Further refinements into rendezvous techniques were practised via Gemini 8’s mission in 1966, with Neil Armstrong successfully docking his spacecraft with the Agena target vehicle – launched just hours ahead of Gemini – to allow for co-ordinated launch profiles of both spacecraft.
This mission profile allowed for a specific, accurate relative position the be attained between the two spacecraft immediately following launch of the chaser vehicle.
Specifically, this made possible a low initial phase angle, or a low angle between the orbital phase of the Agena, and the orbital phase of the Gemini spacecraft. Since this placed both spacecraft closer together immediately following launch, this reduced the amount of rendezvous burns, or phase adjustments.
A year later, the Soviets carried out the first automated, unmanned docking between Cosmos 186 and Cosmos 188, followed by their debut crewed docking in 1969, when Soyuz 4 and Soyuz 5 rendezvous and docked with each other.
This eventually paved the way for the first rendezvous of two spacecraft from different countries, with the historic Apollo-Soyuz Test Project (ASTP) mission in 1975 resulting in an Apollo spacecraft rendezvousing and docking with a Soyuz spacecraft.
“We’ve got Soyuz in the sextant,” noted Apollo pilot Vance Brand, as the two vehicles closed in on each other, pointing to some of the “technology” that was employed in that era.
Advances in rendezvous technology, employed by the two major space fairing nations, were refined via the arrival at space stations, not least with the Russian MIR and during the assembly of the International Space Station (ISS).
In 1995, Atlantis arrived at the Russian outpost using the R-bar or Earth radius vector approach – closing in on MIR from “below” the complex.
This R-bar approach is exactly what Atlantis pioneered on her previous STS-66 mission.
The R-bar approach allowed the use of natural forces to brake Atlantis’ approach to MIR more than a direct approach to MIR would have done. This allowed for minimal RCS thruster firings and the conservation of propellants.
Upon docking, Atlantis and MIR formed the largest orbiting complex ever in orbit – a record which was broken on Atlantis’ next trip to MIR and then stood until the construction of the International Space Station.
The Shuttle fleet conducted rendezvous operations with a number of spacecraft, ranging from satellites to the Hubble Space Telescope. However, it was the ISS that became their main port of call during the latter part of their careers.
Using refined and well practised procedures, orbiters would use inputs from their star trackers and then radar to aid the Digital Autopilot (DAP) approach to the ISS.
Orbiters would then perform the TORVA (Twice Orbital Rate V-bar Approach) maneuver to take the orbiter from the R-bar to the V-bar (Velocity bar) directly in front of the Space Station’s line of travel.
Once properly aligned within the docking cone, the orbiter’s thrusters were pulsed to reduce the orbiter’s speed by two-tenths of a foot per second, effectively slowing the ship and allowing the ISS to “catch up” with the orbiter.
Then, at a much closer range, her thrusters would once again be pulsed to increase the orbiter’s speed by one-tenth of a foot per second, ahead of soft mate docking.
“To put that in perspective for you, we took a quarter-million pound vehicle and connected it with about a half a ton vehicle, and we did that all at 17,500 miles per hour,” flight director Cathy Koerner once said during a Shuttle mission.
The Shuttle fleet are now asleep in their museums, although the ISS continues to lap around the planet, with an array of vehicles bringing crew and cargo to the outpost.
The Russian vehicles, Soyuz and Progress, employ an automated KURS systems for rendezvous with the ISS, with a backup TORU system that allows for manual control.
That switch was recently seen during the arrival of Progress M-21M, when Oleg Kotov took manual control over the resupply ship, following an issue with a more-efficient KURS automated rendezvous system that was being tested during that mission.
The Chinese are still playing catch up, with their first foray into rendezvous operations involving approach and dockings with the Tiangong-1 module.
Shenzhou-10 was the most recent mission to rendezvous with what will eventually lead to a Chinese space station effort. Both automated and manual rendezvous and dockings have been successfully achieved.
Japan’s resupply ship, the HTV, uses RVFS (HTV Rendezvous Flight Software) tied into an array of technology for its arrival at the ISS.
The HTV conducts rendezvous burns to close in on the Station, ahead of using the Proximity Operations (PROX) system, located in the Japanese Experiment Module (JEM) on the ISS, to communicate with the station.
Using PROX, HTV performs an Approach Initiation (AI) burn and, and once it reaches a desired point below the station, it conducts the R-bar Injection (RI) burn.
Once HTV performs the RI burn, it enters the ISS Keep Out Sphere (KOS), following which HTV proceeds to a point 30 meters below the station, and then proceeds to the capture point, thus concluding the rendezvous phase of the mission. It is then grappled by the Station’s robotic arm and berthed.
Aiding the arrival of the spacecraft are sensors on the vehicle, with advances being made on the new fleet of resupply ships that are tasked with missions to the ISS.
Orbital’s Cygnus spacecraft has been using Jena LIDARs (Light Detection And Ranging) sensors for its rendezvous with the Station.
Cygnus will eventually begin to incorporate the use of the TriDAR vision system – designed by Canadian company Neptec, with the support of NASA and the Canadian Space Agency.
This system provides real-time visual guidance for navigation, rendezvous and docking procedures – and was successfully tested as a parting gift from the Shuttle fleet, flying on three missions, namely with Discovery on STS-128 and STS-131, prior to its final shuttle trip with Atlantis on STS-135.
The Shuttle’s also provided a test of the sensor system for SpaceX’s Dragon.
As seen on Dragon’s recent missions to the Station, the vehicle holds at 250 meters distance – following an array of burns and checkpoints during its arrival – where a health check of Dragon’s LIDAR system is conducted.
The system has worked well – bar one slight hiccup with stray reflections from the ISS during her debut arrival. The spacecraft is currently preparing for her fourth mission to the orbital outpost.
ESA’s ATV resupply craft, unlike Cyngus, HTV and Dragon, directly docks with the ISS.
During its rendezvous phase, ATV flies entirely autonomously, without any input from the ground, although the ground monitors the rendezvous.
As the spacecraft moves closer to the ISS, its internal navigation switches from using star trackers, to absolute GPS, to relative GPS at 30km from the ISS, to a laser link at 250m from the ISS, and finally used a video target system which enabled the crew aboard the ISS to monitor the approach in the final phase of docking.
UK company e2v provide the CCD47-20 imaging sensors – which were selected by SODERN as part of the two key systems they delivered for the ATV; an SED16 star tracker, an optical device used for determining the orientation of the spacecraft by measuring its position relative to stars, and a Videometer, a system SODERN developed which is the primary rendezvous and docking sensor for the spacecraft.
The next, and final, ATV to be launched to the ISS, ATV-5 – also known as the Georges Lemaître – will test new rendezvous sensors as it approaches the ISS this summer. This is part of ESA’s goal of allowing future spacecraft to rendezvous with “uncooperative” targets, such as orbiting debris or a Mars sample capsule.
The LIRIS demonstrator – short for Laser InfraRed Imaging Sensors – on the last ATV is what ESA managers describe as the first step towards an uncooperative rendezvous in space.
These sensors will be used to scan the targets – usually in the form of reflectors on the outside of the ISS – while onboard computers processed the data using new guidance navigation and control software. The results will be recorded by hardware inside the pressurized element of the ship.
Rendezvous sensors will also play a key role in future missions, with new vehicles preparing to head into space this decade.
Teams involved with SNC’s Dream Chaser were already testing the spacecraft’s rendezvous with the ISS a few years ago, as she continues to fight for the right to return domestic launch capability for American astronauts.
Work relating to rendezvous with bodies such as asteroids is also progressing, as NASA teams press forward with a mission to rendezvous a crewed mission with a captured space rock in the early 2020s.
Also, Advanced Scientific Concepts (ASC) 3D Flash LIDAR (Light Detection And Ranging) range cameras have already been selected for the OSIRIS-REx planetary science mission that will return a sample of the carbonaceous asteroid 1999 RQ36. The mission – launching in 2016 – is aiming to return the asteroid sample to Earth in 2023.
The advances in a spacecraft’s ability to “see” targets on orbit also benefits people back on Earth, with LIDAR and TRIDAR technology involved in areas ranging from the Agricultural to the Military.
The technology for spacecraft will continue to progress, towards the eventual goal of spacecraft successfully rendezvousing in deep space, per NASA’s roadmap ambitions.
Images: Via L2, ASC, Netpec, NASA, JAXA and ESA).
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