SpaceX Starship Never Stops Thrusting With Hot Staging

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Elon Musk told Ashlee Vance on a Twitter Space, that SpaceX had recently decided to switch to a “hot-staging” approach where the Starship upper stage will ignite its engines while still attached to the Super Heavy booster.

Musk said, describing the switch to hot staging. “There’s a meaningful payload-to-orbit advantage with hot-staging that is conservatively about a 10% increase.” This will be done on the next Super Heavy Starship launch. This was discussed 36 minutes into the Twitter Space.

Hot-staging has been used on Russian launch vehicles for decades. The engines of one stage are ignited while still attached to its lower stage. Musk said that, for Starship, most of the 33 Raptor engines on the Super Heavy booster would be turned off, but a few still firing, when the engines on the Starship upper stage are ignited. Doing so, he said, avoids the loss of thrust during traditional stage separation, where the lower stage shuts down first.

Doing so requires some modifications to the Super Heavy booster. Musk said SpaceX is working on an extension to the top of the booster “that is almost all vents” to allow the exhaust from the upper stage to escape while still attached to the booster. SpaceX will also add shielding to the top of the booster to protect it from the exhaust.

“This is the most risky thing, I think, for the next flight,” he said of the new stage separation technique.

Besides the change in stage separation, Musk said SpaceX made a tremendous number of other changes to the vehicle, “well over a thousand.”

SpaceX was continuing work to upgrade the launch pad to avoid the damage caused by the first Starship launch April 20, such as a “steel sandwich” water deluge system. “We’re actually going for overkill on the steel sandwich and the concrete, so that should leave the base of the pad in much better shape than the last time.”

SpaceX does not spend any time thinking about competition. They only focus on improving their own systems.

If SpaceX luck holds they will launch 80% of the mass of the world’s payloads to orbit this year.

13 thoughts on “SpaceX Starship Never Stops Thrusting With Hot Staging”

  1. smart to let some engines on during the last stage, extremely hard to control and risky to fuel to 32 engines in the last 10 seconds. Blowouts are risky

  2. > Hot-staging has been used on Russian launch vehicles for decades.

    Which were all expendable, I suppose. Doing this with a reusable vehicle may turn out to be much more challenging. Even with protection on the lower stage, the upper stage’s exhaust could still damage it.

    The extension likely isn’t trivial either. It changes the aspect ratio of the stack, which changes how it’s affected by the loads. In the same space, they could add more fuel instead, though I don’t know how that would compare.

    But certainly, let them try, and see what they can learn from it.

    • SpaceX has reused dozens of F9 first stages that had a Merlin vacuum ignite right next to the first stage so I would imagine that they have a really good idea of the thermal stress this places on an oxidizer tank.

  4. Great company, I still wonder how theyll be able to launch on the moon or mars, I know, less gravity needs less thrust but the water system will be harder for the launchpqd. Food for tought.

    • The lunar version on Starship will have Draco engines around the circumference of the ship just below the cargo section. This should allow Starship to land and takeoff without destroying the landing pad.

    • On Mars there is no need for Superheavy. Starship is very effective as a Single Stage To Orbit Rocket there. There likely IS available water they could use for launch pad cooling and noise suppression but it’s likely unnecessary.

    • There’s no booster on Moon and Mars, only the upper stage. That has been launched with no pad problems on Earth, and no water needed IIRC.

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