Some teasing pictures of Stratolaunch
The Stratolaunch website has been revamped, and now shows some teasing images of the giant Stratolaunch airplane.
Doug Messier provides some added details for these images, which really don’t show much.
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 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
The Stratolaunch website has been revamped, and now shows some teasing images of the giant Stratolaunch airplane.
Doug Messier provides some added details for these images, which really don’t show much.
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 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
For RZ:
Question: Does the fact that the “ROC” can fly to 45000 ft traveling hundreds of miles per hour reduce the fuel requirements, and cost, and size of the rocket (for a given orbital altitude and payload) as compared to a conventional ground launch…i.e. is this an improvement in launch efficiency, not just convenience??
md mill: The idea of an airplane for the first stage is that it is reusable and can take off from any runway. Stratolaunch will need a long runway, but nonetheless it can launch from many different places. This gives it a flexibility that vertical rockets do not have.
Whether the cost savings make sense remains an open question. In terms of fuel I think a vertical launch remains overall more efficient.
You need a speed of about 9,000 meter/second in order to remain in orbit. That’s like mach 30 at sea level. Above mach 5 in the atmosphere aircrafts tend to melt by the friction from the air. Air launch today, at just under mach 1, does nothing at all to facilitate take off. It does make launch less weather sensitive, though. Which feels relevant when considering Florida’s bad climate, but Guyana or Baikonur never cancel because of weather.
I generally think that small dedicated launchers will have a very tough time competing with the marginal cost of secondary payload on ever larger and more reusable vertical launchers. And with the 1,000 retired ICBM rocket engines in storage.
Correct me if I am wrong but the Spruce Goose (Hughes H-4 Hercules) has the longest wing span of any aircraft – which has actually flown. Can you imagine what Howard Hughes could have done with modern digital technology and modern materials!
My intuition has always been that the first 60 seconds of a launch (let us assume below 300 miles per hour)
is very inefficient. At lift-off the burn rate of fuel (and thrust) is enormous and the velocity and acceleration are nearly zero…thus mechanical power near zero. What a waste!
If the ROC launches the “Thunderbolt” rocket at 40,000 ft and at 400 miles per hour to start, isn’t this some significant advantage; in short how much more expensive would the Thunderbolt need to be to launch vertically?
I’m sure the rocket engineers have figured this out, but I don’t know. Any rocket engineers out there?
Of course none of it is reusable which is a big down side consideration.
Although the first 2 stages of the Thunderbolt are solid fuel and so “relatively” inexpensive, I would think.
I still believe this is for the military and operational awareness for quick launching of small sats. solid rockets with small sats … launch on demand in any theater
Vladislaw: Perhaps …but a 5 ton (Thunderbolt rocket payload) is a pretty big (mid size) satellite, especially for low orbit .
m d mill asked: “is this an improvement in launch efficiency, not just convenience?” and Robert wrote: “In terms of fuel I think a vertical launch remains overall more efficient.”
I’m not so sure that this is the correct answer. Robert’s direct comparison to a first stage may be unfair, as the design is not to replace the capabilities of the first stage but to take advantage of launch from higher altitude, including reduced air density, and the greater flexibility in launch location.
I am a spacecraft engineer, rather than a rocket engineer, but we can compare the Pegasus air launched rocket to vertically launched rockets of similar payload capability:
Pegasus launches 443 kg to low Earth orbit (LEO). It weighs 23,000 kilograms and is 17.6 meters long by 1.27 meters diameter. (The length may include the payload fairing.)
Brazil’s VLS-1 launches 380 kg to LEO. It weighed 50,000 kg and is 19.5 meters long by 1 meter diameter. (This rocket seems to have used strap-on solid rocket boosters.)
Russia’s Start-1 launches 532 kg to LEO. It weighs 47,000 kg and is 22.7 meters long by 1.6 meters diameter. (The length may include the payload fairing.)
China’s Kuaizhou 1 launches 430 kg to LEO. It weighs 30,000 kg and is 19.4 meters long by 1.4 meters diameter.
Delta 1604 launched 390 kg. (This rocket seems to have used six strap-on solid rocket boosters.)
It looks to me that the air launch reduces the launch weight by 1/4 to 1/2.
My understanding of the advantages of air launch over vertical sea level launch is as follows:
1) Vertical launch starts out using 1 g of acceleration to fight gravity directly (similar to what m d mill pointed out), while an air launch can use a small wing to relatively efficiently convert forward motion into lift. Thus, air launch can use less propellant to accelerate to speed rather than use it to fight gravity or to climb directly upward.
It seems to me that the rocket would need around 1 g less thrust if it is horizontally air launched than if it is vertically launched from the ground. This would save weight and expense on the engines.
2) Air launch is about 5% of the altitude to Low Earth Orbit and can provide almost as much “throw” as the motion of the Earth does. The overall delta-V to attain orbit is reduced. Thus, the propellant tanks can weigh a little less, providing less overall mass that must be lifted and accelerated. Please note that the kinetic energy, due to the acceleration, is about 10 times the potential energy, due to the climb.
3) At altitude, the air density is less than 1/4 of sea level, allowing for less drag forces on the rocket and requiring less rocket propellant to overcome. However, the amount of fuel used by the aircraft could be greater than the amount of propellant saved by air launching the rocket. The rocket’s performance may be better, but it does not include the performance of the aircraft.
Notice that for Falcon, max Q happens about 14 km (45,000 ft), at about 1,800 km/h (1,600 ft/sec or 1,100 miles/h) and about a minute and a half into the flight.
https://www.youtube.com/watch?v=p_qSJbEJsZI#t=95
(m d mill, your assumption of the speed at 60 seconds may be off by a factor of 2, as Falcon 9 seems to be at 600 mph/1000 kph at that time)
For an air launch at 45,000 feet, max Q would happen at a higher altitude, so the maximum force against the acceleration of the rocket would be lower. There is even a proposal to launch from a high altitude balloon, which suggests that the lower air density is a greater consideration than the speed that is gained by launching from an aircraft.
4) The engines can be optimized to be more efficient in space, since it spends its time above 40,000 feet rather than spending its first half minute or so near sea level.
I believe that the advantages that Stratolauch is supposed to provide included the ability to launch larger rockets and more massive payloads than Orbital ATK can launch.
Another factor to be considered is rocket size. Their are limits to the amount of weight carried by existing aircraft, including the Stratolaunch aircraft, so there is a limit on the weight of the air launched rocket.
The larger and more massive the rocket, the more structure will be needed onboard the rocket to support its weight during the winged lift portion(s) of the flight. Non-air-launched rockets are supported in multiple locations when they are horizontal (note that the Falcon 9 pictured in the above link is supported at each end). Also note that they are unfueled, thus lightweight, when horizontal. Stratolaunch has one mount point, at the aircraft’s wing, therefore a larger, heavier, fueled rocket will only be supported by the one mount point. This means that any existing vertically launched rocket would require some redesign in order to be structurally sound during an air launch. The weight of the onboard support structure will reduce the advantage of air launch for large rockets.
Clearly, there is a maximum size or weight of a rocket for air launch to be practical.
Edward– great stuff.
Edward: Very educational. Thank you. It appears that the biggest advantage for air-launch is the reduction of max Q in the atmosphere, something that never occurred to me.
Edward: A belated thanks for the info