IXV Mission Profile Details

Everything is ready in Kourou, French Guiana, for the Vega launch that will start the short mission of ESA’s Intermediate Experimental Vehicle, or IXV. In a previous article we provided some characteristics of the IXV. In this follow on article we discuss the complex mission timeline and we provide some additional details about events that will take place during this important test of re-entry technologies.

Let’s divide the mission in two phases: the launch and orbit phase, and the entry and recovery phase.

Altec’s IXV Mission Control Centre in Turin, Italy. Credits: Altec SpA/Bellomo

Altec’s IXV Mission Control Centre in Turin, Italy. Credits: Altec SpA/Bellomo

Launch and orbit phase
The launch window on February 11 will open at 13:00 GMT and will close at 14:43 GMT. The overall trajectory has been a matter of trade-offs, a credit to Vega launcher flexibility that could have accommodated many different mission profiles at different orbital inclinations. Even full-orbital schemes were considered, because the AVUM could have been used to provide a de-orbit propulsion. The final mission profile will see the Vega launcher bring IXV into a highly elliptical orbit that will simulate a de-orbit trajectory after a mission to the International Space Station.

After launch, the first three stages of Vega will put the AVUM/IXV combination in orbit. The AVUM will then initiate a long burn (close to 6 minutes) to adjust the orbital parameters. At the end of the burn the AVUM/IXV combination will coast until IXV separation.

The AVUM, now flying alone, will perform two more burns, one for separation from IXV and one for a controlled re-entry into the atmosphere over the Indian Ocean. The Vega launcher mission will end with this last AVUM burn.

In the meanwhile, after separation from AVUM, the IXV Reaction Control System thrusters (four, on the aft end of the vehicle) are primed and the GNC system readied for operations, starting attitude control. After separation and before apogee IXV will be in continuous contact with the two African ground stations. The IXV Mission Control Centre in Turin, Italy, will be able to receive real-time telemetries, but flight operations will completely under automated control: there is no command capability provided in the ground segment.

Artistic rendition of IXV during hypersonic entry. Credits: ESA

Artistic rendition of IXV during hypersonic entry. Credits: ESA

Entry and recovery phase
The sub-orbital trajectory will intercept the entry interface, at an altitude of 120 Km, with a very shallow angle of a few degrees and an IXV speed around 26800 km/h. Both conditions are similar to those encountered during a de-orbit from ISS altitudes.

While preparing to approach the entry interface, the IXV will assume a pitch up attitude, very much like how a Space Shuttle Orbiter used to do in the same flight phase. In fact the overall trajectory flown by the IXV will be under guidance algorithms very similar to those used by the Shuttle Orbiter for its hypersonic entry. IXV guidance will target a geographical location and a given altitude (from which the parachute-controlled descent will start) and will follow a drag profile while also verifying the planned rate of descent. Drag control will be roll based: banking the vehicle it will be possible to modify the drag experienced and also correct the trajectory. Pitch control (actually angle of attack) will not be used for this entry profile, but we assume that some kind of pitch profile will be programmed into the descent. Roll control will be initially based on RCS while elevons will start gaining authority since the very early phases of the entry. Because elevons and RCS will not work together, very soon attitude control will be switched to elevons.

During the descent, data from more than 300 sensors will be recorded on board for subsequent analysis on ground. Among the data there will also be a thermal videocamera that will show temperature variations across a wide area of IXV bottom panels, made from high-performance carbon fibres woven into a ceramic matrix pattern for heat resistance and strength. It is expected that IXV will have to withstand temperatures up to 1700°C. During the hypersonic part of the descent a plasma sheath of ionized air will envelope the vehicle creating a communications blackout. The recovery ship will start tracking the expected position of IXV until signals are again acquired. After acquisition, most of the entry profile will be already completed and monitoring will concentrate on the complex braking sequence accomplished with parachutes, while landing coordinates estimates will be received from the IXV GNC system.

The parachute sequence will slow down IXV from supersonic speed (around Mach 2) down to subsonic and then splashdown speed. The entire sequence has been tested in June 2013 with an IXV model dropped from 3 Km of altitude into the Tyrrhenian sea off the coast of Sardinia island. Flotation gear was also tested in the same instance. It looks like it should be possible to watch in real-time the final phases of IXV descent thanks to video cameras installed on the recovery ship. After the IXV has been recovered by the support ship Nos Aries, the residual RCS propellants (hydrazine) will be purged in a safe way.

The PDF file provides a comprehensive timeline of events for the whole mission. Some values may be slightly inaccurate as they have been obtained by different sources. Timings are apparently accurate (after multiple verifications).

We acknowledge the assistance of Mr Alessandro Bellomo (Altec SpA) and Mr. Gianfranco Santoro (ThalesAleniaSpace-Italy) in providing critical information for this article.

F. Bernardini, FBIS

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