NASA’s Cassini spacecraft is making its last five orbits around Saturn, marking the final phase of its mission to explore the planet (it made the first of the five passes over Saturn on 13 August).
The closest encounter between the spacecraft and Saturn will occur when it comes within 1,630km and then 1,710km of the planet’s cloud tops. Cassini is also expected to experience an atmosphere dense enough to require the use of its small rocket thrusters to maintain stability.
NASA will consider the second day of Cassini’s final mission as “nominal” if the thrusters operate at 10-60% of their capability.
If they are forced to work harder, NASA will increase the altitude of subsequent orbits (this is known as a ‘pop-up manoeuvre’, where the thrusters will be used to raise the altitude of closest approach on the next passes by about 200km).
It is planned that Cassini will face a distant encounter with Saturn’s moon Titan on 11 September; this will slow Cassini down, bend its path slightly and initiate its plunge into the planet, which should take place on 15 September.
During the final phase, the spacecraft’s instruments are expected to make detailed high-resolution observations of Saturn’s auroras, temperature and the vortexes at the planet’s poles.
NASA will also try to activate the spacecraft’s seven ‘science instruments’ — including INMS (Ion and Neutral Mass Spectrometer) and reporting measurements — in near real time during Cassini’s half-orbit plunge.
Meanwhile, US-based Space Systems Loral (SSL) has concluded the preliminary design review (PDR) for NASA’s Restore-L mission, which will offer satellite servicing in low Earth orbit (LEO). Completion of the PDR has enabled the mission to move towards its next development phase, which will include a detailed design process.
The three-day PDR was carried out at SSL’s facilities; it demonstrated the mission’s ability to meet system requirements.
SSL government systems president Richard White said: “Satellite servicing in low Earth orbit is of great value for NASA exploration and science architectures, as well as national security. With the PDR successfully completed, we are on track to develop a capability that helps maintain our country’s international position as a leader in advanced space technology.”
To be launched by 2020, the spacecraft will be designed to use robotics and several advanced technologies to grasp and refuel government satellites already in LEO in order to extend their operational life.
It will also demonstrate new tools, technologies and techniques that will help future space exploration missions, as well as a new satellite-servicing industry in the USA.