DARPA HTV-2

DARPA says it lost contact with its HTV-2 hypersonic test vehicle 9min after launch of the dart-like glider atop a Minotaur IV Lite booster from Vandenberg. The agency's brief [Vous devez être inscrit et connecté pour voir ce lien] says the Minotaur successfully delivered its payload to the desired separation conditions and deployed the HTV-2, so telemetry was lost after the unpowered vehice was released at the edge of the atmosphere.

One possibility is that a sheath of plasma that would form around the vehicle as it reentered the atmosphere at Mach 20-plus could have interfered with telemetry. But in an interview with Aviation Week before the flight, DARPA program manager Paul Erbland said the risk of ionized gases attentuating signals from the vehicle was "relatively modest", particulary at the high altitude the HTV-2 was deployed.


The release does not say what happened to the HTV-2 - the vehicle had a specially developed autonomous flight safety system designed to detect any deviation from the planned route and automatically terminate the flight.

The Lockheed Martin-built HTV-2 was supposed to fly 4,100nm across the Pacific in 30min in the first of two flights to demonstrate aerodynamic, thermal-protection, and guidance, navigation and control technology for a prompt global strike weapon able to fly 9,000nm in under 2 hours. The second flight is planned for 2011.

The sharp-edged, highly swept HTV-2 is designed to demonstrate long endurance at high speed by achieving an "unprecedented" hypersonic lift-to-drag ratio, much higher than the Space Shuttle's, and having a carbon-carbon aeroshell that provides thermal protection with minimal ablation, unlike a reentry-vehicle heat shield that burns off to shed heat.

Looking for success among the bad news, DARPA says the Minotaur executed "first of its kind" energy-management maneuvers before releasing the HTV-2. These were required, Erbland said, because even with just three Peacekeeper missile stages, the Minotaur IV Lite is more powerful than required. So the third stage maneuvred to bleed off energy before deploying the HTV-2 at the edge of the atmosphere.

Even then, he said, the booster would overshoot the desired insertion conditions by around 100,000ft, so the HTV-2 was programmed to reenter then pull up to the correct altitude to begin its hypersonic glide - which was planned to start around 200,000ft and Mach 20 and end around 100,000ft with the HTV-2 rolling inverted and pulling down into a hypersonic dive into the ocean off Kwajalein. Well, that was the plan.

Uncovered by the incomparable flateric on [Vous devez être inscrit et connecté pour voir ce lien], this graphic from a [Vous devez être inscrit et connecté pour voir ce lien] by DARPA Tactical Technology Office director David Nyland suggests contact with the HTV-2 (on the yellow Mission A line) was lost somewhere between beginning reentry and starting its hypersonic glide.

Investigation of the telemetry failure is under way. but the question now is what this means for the second HTV-2 flight (red Mission B line above). This is intended to demonstrate the cross-range capability provided by the vehicle's hypersonic aerodynamic efficiency - and key to a prompt global strike weapon - involving sustained maneuvers beyond the simple S-turns planned for the first flight. It's more likely the second flight will have to be a repeat of the first

Deuxième tentative pour le planeur hypersonique de la Darpa

L'agence américaine a perdu le contact avec le HTV-2 alors qu'il venait de franchir la vitesse de Mach 20, durant ce deuxième essai qui s'est déroulé le 11 août dernier.

La maîtrise des vols hypersoniques est encore loin d'être totalement acquise, comme en témoigne le deuxième essai du planeur hypersonique Falcon HTV-2 qui a eu lieu le 11 août dernier.

Comme lors de son premier essai en avril 2010, le HTV-2 de la Darpa a d'abord été tiré au moyen d'une fusée de type Minotaur IV, qui lui a permis de franchir les frontières de l'atmosphère. Une fois séparé de son lanceur il a alors entamé sa rentrée atmosphérique, où il atteint la vitesse de Mach 20 (environ 20.900 km/h).

Cette phase de transition est le point le plus critique du vol. Théoriquement, l'engin doit être maintenu sous contrôle durant tout cette phase d'accélération avant de terminer sa course en vol plané vers un point défini du globe (l'océan Pacifique, en l'occurrence). Théoriquement, car comme lors du premier essai, la communication a été perdue au bout de 9 minutes de vol. Ce dernier aurait normalement du durer trois fois plus longtemps.

Si la Darpa estime avoir aujourd'hui une bonne maîtrise du lancement de l'engin dans l'espace et de son insertion dans l'atmosphère terrestre, elle concède ne pas bien savoir comment garantir ensuite une bonne maniabilité durant la rentrée atmosphérique. D'autant que l'échauffement de l'engin dépasse à ce moment les 1.900°C. Ce qu'il est advenu du démonstrateur après cette perte de liaison n'a pas été communiqué. La Darpa précise seulement que l'engin s'est vraisemblablement abîmé quelques part dans le Pacifique.

Si ce deuxième essai ne peut être qualifié de franc succès, la Darpa se dit néanmoins satisfaite de la quantité de données récoltées sur le vol à vol à très haut Mach. Un troisième essai devrait donc logiquement avoir lieu.

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Le HTV-2 ou "Falcon Hypersonic Technology Vehicle 2" est développé dans le cadre d'une initiative de recherche américaine baptisée "Conventional Prompt Global Strike" (CPGS). Cette initiative vise à terme à la mise au point d'une arme conventionnelle (non nucléaire) capable de frapper n'importe quel point du globe avec un temps de réaction très court (moins d'une heure). C'est également dans le cadre de l'initiative CPGS qu'est développé l'engin à superstatoréacteur X-51A de Boeing.

DARPA releases HTV-2 details

The Defense Advanced Research Projects Agency (DARPA) has released new details about the fate of the Hypersonic Test Vehicle (HTV-2), which crashed into the Pacific Ocean during its 11 August flight.

"An initial assessment indicates that the Flight 2 anomaly is unrelated to the Flight 1 anomaly," said Major Chris Schulz, HTV-2 programme manager.

"We've confirmed that the HTV-2 made impact with the Pacific Ocean along its flight trajectory as planned in the event of an anomaly," Schulz said.

The unpowered glide vehicle was successfully boosted into space by an Orbital Sciences Minotaur IV rocket, and re-entered the atmosphere at M20.0 hypersonic as planned. Three minutes later, the vehicle encountered an as-yet undescribed anomaly and crashed into the Pacific Ocean.

"HTV-2 demonstrated stable aerodynamically controlled M20.0 hypersonic flight for approximately 3min," said DARPA director Regina Dugan. "It appears that the engineering changes put into place following the vehicle's first flight test in April 2010 were effective. We do not yet know the cause of the anomaly for Flight 2."

Flight 1 ended shortly before the 9min mark before encountering unanticipated aerodynamic difficulties that caused it to exceed its flight parameters; its onboard computer automatically directed it into the ocean for safety reasons. As a result several changes were made to the vehicle and its flight path in anticipation of Flight 2.

DARPA has repeatedly declined to release further information in advance of an engineering review board. No date has been set for release of information from the board.