Uncrewed missions to LEO

Not all missions that enter Earth orbit and return carry a crew. Some missions carry experiments to LEO and return them safely. These missions can be flown on uncrewed crewed platforms such as the SpaceX Dragon capsule and the Russian Foton capsule. Others, such as Space Rider and X-37 have been developed especially for an uncrewed mission.

In terms of EDL systems, SUSIE’s fuselage is a lifting body which decreases deceleration loads on its crew and payload. Unlike its smaller predecessors IXV and Space RIDER, which are also lifting bodies but use a large parafoil for landing, SUSIE does not carry any parachutes. Instead, it is designed to perform a propulsive landing after re-entry using landing legs, aerodynamic control surfaces and controllable engines. Ejection seats for the crew are also included in the design. SUSIE can carry up to 5 astronauts or 7 tonnes of cargo inside its 40 m³ cargo bay, both on ascent and on descent [196].

The concept of the Sierra Space Ghost project is unlikely anything else. Yet the technology which is used is not. The Ghost vehicle is designed for rapid on-earth cargo delivery. This is done By leaving these vehicles in orbit for up to 5 years with pre-packed cargo of 250-750 kg [227,228,229,300].

When inserted into orbit, it will already unfold its umbrella-like decelerator. The vehicle starts its deorbit burn once the cargo is required on earth. After re-entry into the atmosphere, it will deploy its parafoil to land within 100m of its target location [228]. With this system, Sierra Space aims to deliver cargo for either military or disaster relief within 90 min [228,229,300].  

The Bion program was started in 1973 to perform biological research. The satellites carried all kinds of biological experiments on various living species ranging from fungi and plants to monkeys and tortoises. On average, the missions lasted 22-days. The return capsule was a modified Zenit-2 re-entry capsule. However, due to the Zenit-2 being a spy satellite, information is rather scarce. What can be assumed is that the cameras from the Zenit-2 were removed to make space for the experiments and also their life-support.

The Bion program ended in 1996 and was followed up by the Bion-M program. This has its first flight in 2013. This re-entry capsule is based on the Vostok capsule (link to chutes Vostok page). The capsule was also modified for biological experiments. However, compared to the original Bion experiments, the experiment's lifetime was extended to 6 months, and the scientific payload was increased by 100 kg. However, the first Bion-M mission only had a mission duration of one month. The second Bion-M mission was scheduled to be launched in 2020 but was delayed until 2023. [20, 21]

While CORONA satellites had carried one or two film return vehicles, HEXAGON carried four, or five when the optional mapping camera was used. It was able to achieve a ground resolution of under 2 feet (0.61 m).[222] This and other improvements meant that HEXAGON was much heavier, weighing 11,400 kg and requiring the use of Titan IIID or Titan 34D rockets. Each of the McDonnell-Douglas Mk 8 recovery vehicles weighed 434 kg and contained up to 23.6 km of film [223]. The film was exposed in the cameras and then returned to Earth inside the capsule to be developed on the ground.

The film return vehicle, or ‘bucket’, had a thermal control system to keep the sensitive film at the right temperature, as well as attitude control thrusters and retro-rockets for deorbiting. A heat shield protected the capsule during re-entry, and at an altitude of 50,000 ft (15 km) it deployed a parachute. A battery-powered radio beacon broadcasted its location to recovery aircraft, which was to catch the vehicle in mid-air. In case the aircraft was unable to do so, the bucket could float and would be picked up by a ship or helicopter, before sinking to avoid the film falling into the wrong hands. The first HEXAGON’s third film bucket, launched in 1971, was not caught when its parachute snapped off. It sank to a depth of nearly 5 km before being recovered by the submersible DSV-1 Trieste II the following year. Sadly the film had by then degraded too much to recover any useful images, though it was the deepest successful salvage operation in history up to that time. The parachute, whose suspension lines had failed due to improper design and the Goodyear engineers having failed to account for the deployment shock load, was replaced by a new ‘extended skirt’ design by Para Dynamics. The drogue chute was also replaced by a new design made by the Irving Air Chute Company. The second HEXAGON launch in 1972, while delayed by all this redesign work, worked perfectly and all four buckets were recovered [224].

The Corona – Discoverer program was one with many failures and challenges that had to be tackled because of the fact that rocketry and satellites were a relatively new and unexplored territory of engineering. One of the early flights, Discoverer-8, encountered a failure that was attributed to the recovery system, where the parachutes failed to deploy, leading to a loss of the vehicle.  It was Discoverer-13 that successfully launched, entered orbit around the Earth and became the first man-made object to be recovered from Earth orbit in 1960, only 9 days before the USSR achieved the same result with one of the Sputnik probes. Although considered successful, the capsule's recovery didn’t go as planned: the capsule landed too far from the recovery aircraft and had to be quickly recovered by helicopter before it sank. The first mid-air recovery of the corona capsule was Discoverer-14.

Although many flights never returned safely or even didn’t reach space, the Corona satellites managed to provide valuable footage of the USSR. After the last flight of a Corona spy satellite, in 1972, the KH-9 Hexagon spy satellite continued to provide footage for the United States. The satellite carried multiple corona-like capsules that it could deploy at different moments in time. [30, 31, 32]

Much like the US Corona and the Soviet Zenit satellites, China had their own recoverable satellite called Fanhui Shi Weixing. Their main objective was to act as spy satellites, later variants also served as biosatellites much like the Soviet Bion capsules. One interesting feature was the thermal protection of the FSW satellites, this was done using impregnated oak. This allowed for quickly produced ablative thermal protection. 

The FSW satellites also briefly served as the baseline for China's second crewed capsule after the Shuguang spacecraft was cancelled. However, some sources suggest that this program was solely for propaganda purposes and never designed for operation. 

The CARINA Space System (CApsula di RIentro Non Abitata [138], meaning ‘uninhabited re-entry capsule’) was a project of the Italian Space Agency (Agenzia Spaziale Italiana, ASI) that was started in 1990 [139] with the aim of developing a spacecraft that could carry microgravity experiments into orbit and return them to Earth. The spacecraft, which would have had a lift-off mass of approximately 600 kg, would carry up to 165 kg worth of experiments into a 360 km orbit [138]. While in orbit, the experiments would be supported by a service module. Five days into the mission, the vehicle would perform a deorbit manoeuvre, and the service module would separate at an altitude of approximately 130 km [138]. The re-entry capsule, which was of the blunt body type, would safely carry the experiments through the atmosphere until the speed had decreased enough for the parachutes to be deployed, after which the vehicle would splash down in the Indian Ocean [138]. No further information about the parachute system is known, and the project was cancelled in 1995 [139].

From TechEdSat 3 onwards, they include a passive exo-atmospheric de-orbit device, or in simpler terms, a parachute to be used in space environments for de-orbit, named Exo-Brake. This mylar parachute is deployed from the back of the satellite, aiming to replace the more complicated de-orbit systems, like thrusters, for small satellites. IT has a cross-shape and is supported by a hybrid system of mechanical struts and flexible chord. From TechEdSat 5 onwards, a control system was included that allowed the shape to be controlled in flight, much like the wright brothers did on their initial wing design [33]. The space-parachute onboard TechEdSat 5 had a size of approximately 0.35 m² and has a cross-shape.

The latest iteration TechEdSat, launched in 2020, has the largest Exo-Brake to date [37]. The Exo-brake can now be controlled from the ground to achieve a targeted re-entry and landing location. This should be useful for the de-orbit of satellites and sample return missions.