The launcher to be used to launch the P5-A into a Mars trajectory is under investigation at AMSAT.
During the interplanetary cruise, which will last 6 to 8 months depending on the Earth/Mars constellation at time of launch, ARCHIMEDES will be held in hibernation mode for most of the time. Power, thermal control and data relay will be provided directly through P5-A.
The AMSAT P5-A is planned to have a highly eccentric orbit with a pericentre altitude of some 4 000 kilometres and an apocentre altitude of 20 000 kilometres. This type of orbit provides a sufficiently long visibility time for the ARCHIMEDES Mars entry mission allowing to transmit data in real-time from ARCHIMEDES to the P5-A.
Once the desired orbit around Mars is achieved and visibility between the ARCHIMEDES and the orbiter is ensured for the ARCHIMEDES Mars mission duration, the P5-A will change its orientation and spin up. The separation of the JPS with ARCHIMEDES will be prepared. The ARCHIMEDES batteries will be charged and a system health check will be performed. The trajectory of the spacecraft will be exactly measured in order to determine the most favourable point in time for separation of the JPS with ARCHIMEDES, depending on the desired entry trajectory and angle, which must be very accurately determined, and of the corresponding point in time and position of the spacecraft at time of separation. This is important, since the P5-A orbiter must be visible from the ballute during entry and descent down to the Mars surface in order to allow transmitting data to the orbiter.
The Joint Propulsion System (JPS) with ARCHIMEDES will then separate from the orbiter and autonomously perform a de-orbit manoeuvre, decelerating to the pre-determined Mars entry trajectory.
Starting with separation of the JPS from the P5-A, spacecraft scientific and ARCHIMEDES system health data will be transmitted to the carrier spacecraft orbiting Mars, for direct or later transmission to Earth. The radio link will allow determining the ARCHIMEDES trajectory throughout its mission through radio-ranging.
Once on the desired entry trajectory, the JPS will de-spin and then deploy and inflate the ballute. Then the JPS will be jettisoned. From this point in time onwards until contact with the Mars ground the ballute follows the pre-determined trajectory, leading to entry and descent, in an uncontrolled manner. Roughly six and a half hours later, the ballute will cros the high Mars atmosphere for a first time and be decelerated to a slightly lower Mars orbit. After a number of consecutive passes through the atmosphere will the ballute finally enter into a descent trajectory and begin its descent to the surface. This incremental deceleration of the ballute is mandatory in order to avoid overheating of the ballute, and requires to reach a very accurate approach and entry trajectory and angle.
The P5-A satellite will remain in orbit, receive the ARCHIMEDES data and provide a radio link to ground stations. Vital mission data can therefore be transmitted during approach and descent and will thus be available even in the case of a major malfunction during entry.
After sound barrier transition, the protective nose cover assembly of the ballute with the two entry experiments will be jettisoned, and the instrument pod will be exposed to the Martian atmosphere allowing to begin with atmospheric measurements and taking images of the Mars surface.
The balloon will descent to the ground while continuing to collect atmospheric and magnetometer data and taking images from Mars. This will allow researchers back on earth to establish the first directly measured altitude profile of the Martian atmosphere ranging from the ionosphere right down to the ground.
If successful, these would be the first measurements and data ever taken from an altitude of 50 – 60 kilometres until ground contact.