Why is Sierra Space’s Dream Chaser spacecraft not ready for flight?
In a press release posted last week Sierra Space proudly announced that its Tenacity Dream Chaser mini-shuttle has completed its pre-launch ground vibration tests at the Kennedy Space Center in Florida, but instead of moving the mini-shuttle to a local facility where it could be integrated with its rocket for launch, the company announced it was shipping it back “to Colorado for final modifications and mission-specific upgrades.”
Normally when a spacecraft, satellite, or any payload passes these last ground tests, it is ready for launch, and it immediately begins integration onto the rocket that will carry it into space. That Sierra Space is not doing this strongly suggests Tenacity did not pass with flying colors, and that some issues were identified that need correction.
Note too that this spacecraft had been delivered for these tests in early 2024, and had been expected to pass them then and be launched that year. Instead, months passed with no word, then its launch was postponed indefinitely, and then NASA canceled Sierra’s contract to provide cargo to ISS.
Now, two years later Tenacity is still not ready for launch. Though the company says the ground tests are now complete, I suspect otherwise. I suspect there is some fundamental issue with the spacecraft that they are hiding because to reveal it would be devastating to Sierra’s public reputation.
Until we know more however this is pure speculation on my part. What we do know however is that this mini-shuttle has not done what was promised, and increasingly appears to be a lemon that will never do it.
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"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
In a press release posted last week Sierra Space proudly announced that its Tenacity Dream Chaser mini-shuttle has completed its pre-launch ground vibration tests at the Kennedy Space Center in Florida, but instead of moving the mini-shuttle to a local facility where it could be integrated with its rocket for launch, the company announced it was shipping it back “to Colorado for final modifications and mission-specific upgrades.”
Normally when a spacecraft, satellite, or any payload passes these last ground tests, it is ready for launch, and it immediately begins integration onto the rocket that will carry it into space. That Sierra Space is not doing this strongly suggests Tenacity did not pass with flying colors, and that some issues were identified that need correction.
Note too that this spacecraft had been delivered for these tests in early 2024, and had been expected to pass them then and be launched that year. Instead, months passed with no word, then its launch was postponed indefinitely, and then NASA canceled Sierra’s contract to provide cargo to ISS.
Now, two years later Tenacity is still not ready for launch. Though the company says the ground tests are now complete, I suspect otherwise. I suspect there is some fundamental issue with the spacecraft that they are hiding because to reveal it would be devastating to Sierra’s public reputation.
Until we know more however this is pure speculation on my part. What we do know however is that this mini-shuttle has not done what was promised, and increasingly appears to be a lemon that will never do it.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The print edition can be purchased at Amazon or from any other book seller. If you want an autographed copy the price is $60 for the hardback and $45 for the paperback, plus $8 shipping for each. Go here for purchasing details. The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
I spoke with some Sierra Space folks at the Space Symposium this year. They’re focusing on customers other than NASA (i.e., DoD?), so I suspect that means they’re putting some other kind of payload on board, rather than cargo for the ISS.
Ballonman: Of course they aren’t putting ISS cargo on Tenacity. NASA canceled their contract in September 2025. Whether they have found any other customers remains unknown.
The real question is why this spacecraft still needs “final modifications?”
“That Sierra Space is not doing this strongly suggests Tenacity did not pass with flying colors, and that some issues were identified that need correction.”
Yeah, it’s hard to see how this could be a good sign for how it fared in testing.
It does seem increasingly likely Dream Chaser will never fly. It hardly helps matters that its would-be launch vehicle, Vulcan, is also hors de combat at the moment.
This makes me sad because gliding back from orbit and landing on a runway is elegant and super-cool. Somebody should strap some wheels on Starship and build a runway at Starbase. There I said it.
Winged spaceflight needs its own tech-bro.
Help me Woz…you’re my only hope.
It isn’t flying because it doesn’t have to.
No one there cares. Well no one who has the power to do anything about it.
” . . . suggests Tenacity did not pass with flying colors, . . .”
I suppose those are the only colors that matter.
From the press release:
It is reasonable to believe that Tenacity has some punch-list items left to complete. For instance, the cargo module still has to be attached before launch. Since the mission for first flight is a hardware checkout without approaching ISS, I’m not sure what “mission specific” upgrades are needed. Maybe they want to add some instrumentation to measure performance during this first flight. Back when I was building and testing satellites, we always seemed to have some final touches to do after the last test and before packing the spacecraft for shipment to the launch site. “Modifications” is a funny way to phrase it, as though there are changes to be made, not batteries or doodads or whatever to be installed as final assemblies.
What caught my eye was that the press release said that there were several key milestones achieved, not that all the environmental testing was complete. Is there anything left to test? Maybe even a final post-environmental wing deployment test?
If the modifications are minor, then one would expect an announcement of an expected launch date or month.
RocketLaunch.Live has Dream Chaser listed as launching on a ULA Vulcan sometime in 2026 but gives no specific date, month, or quarter. I do not discount the possibility that Sierra Space does not want to launch on a Vulcan until the SRB issue is resolved satisfactorily. With NASA’s modified contract, there does not appear to be any rush for Sierra Space to reach space, so there is no reason to take a risk on a Vulcan until that rocket is operating more reliably — without “observations.”
My recollection is that Falcon’s fairing is not large enough for Dream Chaser, and New Glenn has not yet proved itself reliable, either.
Edward wrote, “It is reasonable to believe that Tenacity has some punch-list items left to complete.”
You might be right but I have grave doubts. When Sierra delivered Tenacity two years ago for final ground testing, the company was bluntly saying it would launch by the spring of 2024. I don’t think the company would have been so confident about launch if it had these “items left to complete.” And if it did, it has had two years to complete them, and hasn’t.
I think these items are issues that turned up in that testing, and are the reasons the launch never happened and NASA cancelled Sierra’s ISS cargo contract.
Vulcan’s current difficulties provide a convenient excuse for why Dream Chaser isn’t going directly into a payload fairing. If Vulcan straightens up and flies right at least a couple of times by year’s end, though, that excuse goes away. I think if Dream Chaser does not fly within the next 12 months, it’s never going to fly at all.
“Vulcan’s current difficulties provide a convenient excuse for why Dream Chaser isn’t going directly into a payload fairing. If Vulcan straightens up and flies right at least a couple of times by year’s end, though, that excuse goes away.”
Just so.
But if Sierra Space is trying to push off blame for the delay on Vulcan’s struggles — and it’s not entirely clear to me that they’re pushing that — all I can say is that NASA by its own account “restructured” the Dream Chaser contract into just a orbital test flight for reasons that went beyond anything to do with its putative launch vehicle.
But I do not think Dream Chaser is anywhere close to being ready to fly. Everything seems to point to substantial work yet to be done. It’s been difficult to get any detailed information on just exactly where the program stands, but the few ex-Dream Chaser engineers I’ve seen speak out publicly about their experience on DC all point to a program that’s been badly under-resourced and badly managed. If that is true, I find it hard to believe that this has really changed.
Richard M wrote: “It’s been difficult to get any detailed information on just exactly where the program stands, but the few ex-Dream Chaser engineers I’ve seen speak out publicly about their experience on DC all point to a program that’s been badly under-resourced and badly managed. If that is true, I find it hard to believe that this has really changed.”
As I recall, Sierra Nevada spun off Dream Chaser to a startup subsidiary company, Sierra Space, specifically because Sierra Nevada did not have the resources and revenue to do the job in a timely manner. The company depends heavily upon milestone payments to keep Dream Chaser moving. I don’t know how the company financed its Life module for the Orbital Reef space station project.
However, if lack of funds is the reason for the slow test program, then why would NASA cancel the cargo missions to ISS? All they have to do is wait another year (more or less) until these begin to fly. On the other hand, if NASA cancelled the cargo missions because they think Dream Chaser won’t work, why are they funding this last flight-test milestone? If the flight test shows that it will work, will NASA reinstate the cargo missions, and if so, why were they cancelled in the first place? This whole thing is confusing especially the part where Sierra Space had enough money to fund the Life module development for a few years.
What is happening with Dream Chaser is difficult to determine. It does not look like a funding issue is causing delays. It does not look like routine punch-list items are causing delays, because that would be a lot of last minute items. It could be lost confidence in the Vulcan launch vehicle, but that would not explain the change in NASA’s contract.
It could be some more major item that needs correction, something so major that NASA lost confidence that Dream Chaser can perform the job, which would explain the changed contract.