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The Falcon 9 first stage is making two or three burns for descending:

  • boostback burn (optional, depends on return to launch site vs ocean landing)
  • entry burn
  • landing burn

But how many burns is the New Shepard doing?

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    $\begingroup$ Nice hat! We have similar tastes. $\endgroup$ – Camille Goudeseune Dec 17 '20 at 21:56
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The Falcon 9 first stage is making three burns wile descending:

Nope. It is making two burns while descending.

  • boostback burn
  1. This burn happens while the rocket is still ascending.
  2. This burn only happens for return-to-launch-site landings. For ASDS landings, it doesn't need to "boost back", because it isn't going back, it is going forward. (They could theoretically do a "braking burn" to reduce the downrange distance for missions where they don't have enough propellant to boost back to the launch site, but more than they need for an ASDS landing, but they don't appear to be doing that. They either boost all the way back to the launch site, or let the ballistic trajectory carry them all the way downrange.)
  • descent burn

This is called the entry burn.

Its purpose is two-fold:

  1. It is slowing down the rocket before it hits the denser parts of the atmosphere.
  2. The engine exhaust actually creates a layer of cooler air around the lower part of the rocket that protects it from the hot plasma. Yes, you read that right: the engine exhaust is still cooler than the plasma created by reentry heating!

Note that this might technically count as two burns, depending on how you define the term:

  1. First, it lights only the center engine.
  2. 3 s later, it lights another two engines.
  3. Another 17 s later, it shuts those two engines down again.
  4. And another 1.5 s later, the center engine shuts down.

But how many burns is the New Shepard doing?

One. It doesn't need to "boost back", because it never went anywhere in the first place, it is just going straight up. And it doesn't need the entry burn because it is never going nearly as fast as a Falcon 9. Again, it never goes anywhere near orbit, it just barely coasts up to the Kármán line and falls down again.

Its maximum velocity on ascent is 1000 ms, on descent, it never goes past 1165 ms and at engine relight, it has slowed down to a measly 165 ms using only aerodynamic drag. [All numbers from the official webcast of NS-13.]

In comparison, the Falcon 9 first stage booster goes up to well over 2150 ms on ascent, and roughly 2200 ms on descent, which is when it fires the entry burn and slows down to ~1200 ms. The landing burn is fired at ~190 ms. [All numbers from the Flight Club simulation of Starlink L-15.]

In other words, New Shepard never even reaches the velocity that F9 has after slowing down using the entry burn.

New Shepard does most of its deceleration using its aerodynamic devices. In particular, if you watch the velocity during one of their webcasts, deploying the drag brake is almost as if they were pulling the handbrake at highway speeds.

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  • $\begingroup$ I modified the question to mention the boostback was optional before seeing you'd just answered and addressed that point. Do you think I should remove that part of the edit or is it okay as it stands? $\endgroup$ – uhoh Dec 18 '20 at 0:08
  • $\begingroup$ @uhoh the general StackExchange etiquette is that questions should be edited to add context or improve clarity, but not to change what the question is, especially if that would invalidate existing answers. If you have a wrong assumption in your question, then that's likely part of why you asked the question, and will be cleared up in the answers. $\endgroup$ – Gavin S. Yancey Dec 18 '20 at 10:29
  • $\begingroup$ Great answer, will you post it again as an answer for the question "How many burns has a Falcon 9 booster for return?" ? $\endgroup$ – Joe Jobs Dec 18 '20 at 10:55
  • $\begingroup$ @GavinS.Yancey ya in this case I've edited a few of the OP's questions already to save them from closing and so that they can receive good answers. In addition to generalizations we can also take history and context into account when deciding what to do in any given case. When I arrived at this page there was no answer so the impact was minimal, but by the time the edit was finished this answer had just been posted. Since the edit had other changes besides the boostback parenthetical I decided not to roll back but instead leave it up to the OP and to the author of this answer to decide. $\endgroup$ – uhoh Dec 18 '20 at 10:55
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    $\begingroup$ @uhoh fair enough. I wasn't looking closely and mistook you for OP $\endgroup$ – Gavin S. Yancey Dec 18 '20 at 21:38
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Only one burn, just before landing, according to Blue Origin's broadcast of NS-12's flight. The only events during climb relating to engines are liftoff and MECO (main engine cut off). After apogee, 45:00 in the video, T+4:45, the only events at all are wedge fins deploy, drag brake deploy, booster restart, and booster touchdown.

(Here are photos and discussion of its wedge fins and drag brakes.)

Displayed telemetry of the descending booster's speed, and a lack of visible exhaust plume despite seeing plenty of detail of the booster itself, confirm that no other burns happened during descent.

Falcon 9 might also have needed only one burn while descending, had it ever flown roughly straight up and down instead of pushing a payload sideways into orbit.

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