The Boeing Delta IV Heavy is going somewhere--but whether that is Earth orbit, the Moon, Mars or market oblivion is an open question
Boeing is preparing a range of Delta IV Heavy launcher options for NASA Crew Exploration Vehicle (CEV) and unmanned cargo transportation architectures to the Moon and Mars, now that the massive new rocket has been flight tested.
The Dec. 21 launch of the 232-ft. vehicle on 2 million lb. thrust marked the largest all-liquid expendable booster flown since the last Saturn V in 1973. A second Delta IV Heavy mission is scheduled for this summer carrying a U.S. Air Force missile warning satellite. The first launch carried a dummy payload (AW&ST Jan. 3, p. 23).
Boeing wants NASA to consider the Delta IV Heavy for manned CEV missions, but is also pushing the Heavy for unmanned exploration launch roles. One Delta IV Medium version could also be a CEV player.
Boeing says even modest upgrades could double the Delta Heavy's Earth orbit capability to more than 50 metric tons, including being able to fire up to 20 metric tons on escape trajectories to Mars.
The current Heavy, like that tested in December, can already send about 10 metric tons to the Moon, while modest upgrades could more than double the lunar tonnage. NASA is asking all exploration program elements to standardize on metric ton references.
Flying supersonic more than a minute after liftoff (far left), the Delta IV Heavy trails fiery, 400-ft. orange plume and miles-long vapor trail. Pitchover aligns trajectory and places critical plumbing out of high-velocity aerodynamic flow.Credit: WILLIAM G. HARTENSTEIN PHOTOS
Also among the options (see chart p. 50) are performance upgrades using new upper-stage engines--including the Pratt & Whitney RL60 and the Mitsubishi/Boeing MB-60.
But the Delta IV Heavy is blazing into unknown territory. And the "unknowns" for this vehicle span all the way to the Moon and Mars--and possibly oblivion in the U.S. launcher stable, if future military and exploration payloads instead use smaller Delta Medium vehicles or the Lockheed Martin Atlas V.
The IV Heavy is also competing against shuttle-derived or still proprietary commercial concepts, including options that might use the Delta IV's RS-68 engines. So, while a powerful and advanced new launcher, the Heavy remains in search of a role more robust than the limited military and commercial markets that brought it into existence, initially as a U.S. Air Force demonstration.
No matter what its future holds, the IV Heavy flew one of the more spectacular first flights in the storied history of rocketry at Cape Canaveral. And the pictures here show some unusual characteristics of the vehicle.
Delta IV Heavy ignites on pad with flaming violence (center) as 100-ft. cloud of burning hydrogen engulfs the 232-ft. vehicle. The massive 330-ft. mobile service tower is in the background.Credit: WILLIAM G. HARTENSTEIN PHOTOS
The Delta IV is the only launch vehicle that, by design, sets itself on fire during its ignition sequence (see center photo).
Thousands of pounds of hydrogen are dumped through the vehicle's three RS-68 engines to condition their internal temperatures 5 sec. before oxygen valves are opened for ignition.
The hydrogen forms a cloud around the vehicle that is burned off by Pad 37 spark generators to avoid an explosive hazard.
This causes a huge ball of fire that blackens the core and the 125-ft. liquid strap-on boosters.
[Hmmm -- hydrogen fuel cell enthusiasts keep telling us that there is no risk of explosion !]
During climbout, free hydrogen continues to attach itself to the base of the vehicle, where it burns on insulation designed for that purpose. So while the fire is inconsequential, parts of the boattail remain ablaze until ascent into thinner air (see photo p. 51).
Its core and liquid strap-on stages blackened by ignition (right), the Delta IV Heavy climbs out on 2 million lb. thrust gulping 3 tons of propellant per sec.Credit: WILLIAM G. HARTENSTEIN PHOTOS
Heat emerging from RS-68 fuel turbine exhausts for roll control can also cause flame on the insulation as with the center engine just after liftoff (see right photo). All of this looks frightening, but is normal.
The overall initial flight test was a success, but Boeing and the U.S. Air Force continue to examine ways to work around a liquid oxygen propellant line bubbling characteristic discovered during the last seconds of the strap-on and core propulsion phases.
The phenomenon tricked measurement sensors in the liquid strap-ons and core to command shutdowns of the three RS-68s about 8 sec. prematurely.
That resulted in the low orbit for a 6.5-ton dummy payload and the loss of two 50-lb. USAF/university student microsatellites. But neither the Air Force nor Boeing believes that a fix to the characteristic will be a serious downstream problem. It was caused by a unique combination of vehicle acceleration, flight path angle and tank and line pressures, according to the Air Force.
Among the range of existing vehicles that could be selected by NASA for the exploration architecture, the Delta IV Heavy is the only new "heavy" rocket to have actually been flown.
Delta IV Medium and Heavy upgrade options have payload mass for each as a symbol on the line under each configuration. The number of graphite epoxy solid motors (GEMs) added to liquid configuration is shown, as are Mitsubishi/Boeing (MB) and Pratt & Whitney (RL) upper stage configurations in addition to the RS-68 first stage engines. Aluminum lithium (Al-Li) structures are indicated, as are regenerative nozzle (Regen) retrofits, propellant crossfeed (X-Feed) and densified propellant (Dens) capability.
The diversity of manned and unmanned heavy versus smaller medium launchers needed for the exploration program, however, will depend upon the outcome of initial NASA architecture studies due later in 2005. Actual booster selections will take longer.
The formal CEV request for proposals NASA is to issue in early March will call for a four-person CEV launch mass no greater than 20 metric tons (44,000 lb.). In comparison, the earlier three-person Apollo Command/Service module needed for Earth orbit and lunar missions had a launch weight of about 67,000 lb. topped by an 8,000-lb. launch escape tower, 34 metric tons total.
The standard Delta IV Heavy, like that shown during its first flight here, would satisfy the initial 20-metric-ton CEV weight target with at least 4,000 lb. of margin to spare.
Upgraded versions of the Delta IV Medium and Lockheed Martin Atlas V medium vehicles would also be candidates for just the CEV launch portion of the new architecture, but not necessarily address the large unmanned cargos that will also need launch.
Any medium launcher options for CEV would, however, have to be equipped with more solid rocket boosters than have been flight tested on either the new Atlas or Delta vehicles. For example, the Atlas V 551/552 medium vehicle with five solids and the Delta IV Medium with six would be needed to satisfy the minimum performance required to launch the 20-metric-ton CEV.
Boeing will be adding the six-solid version to its chart to bridge the capability between its current Medium with five solids and the initial Heavy with three liquid common core boosters and no solids. The Medium designations on the option matrix relate to the diameter of the upper stage for propellant loads (4 or 5 meters) and then the number of solid motors.
Whether any of the Delta or Atlas Evolved Expendable Launch Vehicle options will be acceptable for the CEV manned role remains to be seen.
The Astronaut Office at the Johnson Space Center is not keen on any of these options (AW&ST June 14, 2004, p. 15). The astronauts have taken a position that "human rating should be designed in, not appended on." The Office is calling for an order of magnitude reduction in the risk of fatalities on ascent, and has expressed concern that an EELV--be it Delta or Atlas--may not be safe enough even with upgrades.
"Even with extensive modifications, the EELVs may never achieve a meaningfully higher success rate," the Astronaut Office assessment stated.
Upgrading EELVs "could potentially be as costly as building a new human-rated booster," said the Astronaut Office paper, and still "would place excessive burden on abort mechanisms to save the crew."
The concern in part is due to the potential for rare, but instantaneously catastrophic, failure modes inherent with solid rocket boosters on the medium options for both Atlas and Delta EELVs. Such failure modes would be difficult for an advanced health-monitoring system to catch before loss of control to separate the CEV safely.
Propulsion systems that are human-rated from the start already include the shuttle solid rocket boosters and space shuttle main engines (SSMEs) that could form a shuttle-derived vehicle--a key player in architecture studies.
Boeing is fully aware of the astronaut concerns, says Jim Harvey, who heads Boeing Launch Services development and is leading Delta IV exploration studies. "Instead of a human-rated rocket, Boeing is talking about a 'human-compatible' launch vehicle," Harvey said. And that approach, coupled with CEV escape designed in from the start, he said, would make the whole system human-rated.
Aside from its IV Medium with six solids, Boeing believes its all-liquid propulsion, with more benign failure modes than solids, argues for strong consideration of the Delta Heavy for the CEV role.
The development of health-monitoring capability for liquid engines is well underway in NASA and industry. Such systems are designed to discern if a liquid engine is close to a potential failure that would make separation of a manned CEV less of a challenge.
Upgraded Delta Heavy options do include solids as augmentation to the three RS-68s, but the options with solids would be for only unmanned cargos.
Boeing believes one benefit of using the Delta Heavy for both human or unmanned payloads is the massive Delta IV infrastructure already in place here. The facilities include a 250-ft. fixed service structure and a 330-ft. mobile service tower that can access complex payloads throughout most of a countdown. The Delta IV vehicles and infrastructure combined already represents "billions" of dollars of investment by Boeing, the company says. That infrastructure would need minimal modification to support basic CEV or unmanned exploration missions, Harvey said.
Flaming hydrogen attaches to base of vehicle burning on insulation designed for the phenomenon. Center RS-68 fuel turbine exhaust port also flames on insulation.Credit: WILLIAM G. HARTENSTEIN
"We think that a new system like the Delta Heavy already developed with a lot of growth potential is a real benefit for the overall exploration initiative. It would make it affordable and sustainable," says Frank Slazer, director for NASA and civil space business development at Boeing Launch Services.
"WHY SHOULD THE exploration program pour money into more expensive rocket developments when something like the Delta IV Heavy and its infrastructure already exist?" Slazer asked.
It's an open question at NASA, but Lockheed Martin does not agree. It has its own Atlas V Heavy triple-barrel design. Lockheed Martin says an Atlas V Heavy could be developed within about two years of any government order.
The Atlas V Heavy would look similar to the Delta IV Heavy, but instead use Energomash/Pratt & Whitney RD-180 oxygen/kerosene engines. The Russian engines are now assembled near Moscow, but are slated for coproduction at Pratt's West Palm Beach, Fla., facility by about 2007. Like the RS-68s, the 860,000-lb.-thrust RD-180s have a 100% safety record.
But Boeing notes the Delta Heavy's 650,000-lb.-thrust RS-68s use higher energy oxygen/hydrogen propellants, are relatively simple and could also be used as an upper-stage engine for a translunar stage in exploration architectures. The RS-68 is the first new large rocket engine built in the U.S. in 25 years, and has 80% fewer parts than an SSME.
Boeing also notes that the Atlas V Heavy remains just a "paper rocket," while the Delta IV Heavy has already flown a largely successful test, and has a second launch this summer to carry a Defense Support Program missile warning satellite. Other USAF IV Heavies are slated to launch the heaviest new military satcoms and signal intelligence satellites.
The IV Heavy as flown in December has a 22-metric-ton capability to low Earth orbit that can be advanced to 25 metric tons with no hardware changes. This would be done by flying a more depressed trajectory downrange of Cape Canaveral, Harvey said.
To satisfy USAF range safety requirements for that payload increase, however, Boeing would have to gain USAF cooperation to implement new vehicle monitoring and destruct capability for depressed trajectories that would fall below the horizon of the Antigua tracking station.
Delta IV Heavy upgrade options can be mixed and matched to various exploration mission architectures. The options that can use the existing pad infrastructure include:
*New upper stages: Depending upon the upper-stage cryogenic propellant load desired, the current Heavy uses either a 4- or 5-meter-dia. upper stage with a 25,000-lb.-thrust Pratt & Whitney RL10B-2 engine.
For larger payloads, however, Pratt is well into testing its new RL60 upper-stage engine that, when mated with the Delta Heavy, can begin to push the Earth orbit capability to more than 40 metric tons.
Likewise, Boeing and Mitsubishi are examining a U.S./Japanese MB-60 with about 60,000 lb. thrust. The RS-68 first-stage engine could also be used as a translunar-stage engine, under some Boeing studies.
*Solid rocket booster additions: The addition of four ATK Thiokol GEM-60 solid rocket motors, two on either side of the core, would boost Heavy unmanned Earth orbit payload performance to more than 30 metric tons and escape payloads to 12 metric tons.
Boeing has examined other Heavy unmanned cargo options using six solids to achieve in excess of 50 metric tons to orbit. Each GEM-60 has 191,000 lb. of liftoff thrust and, by mounting them all on the same side, the vehicle can still use Pad 37 without changes.
*Propellant crossfeed: Each Common Booster Core in the current Heavy uses its own cryogenic oxygen and hydrogen tanks to feed its own RS-68. But Boeing is studying a crossfeed system that would allow oxygen and hydrogen from the strap-ons to be pumped into the core also during ascent.
By doing this, the outboards could be loaded with even more propellant than they used in December, but expend that propellant through both their own engines and the core engine. This would use that propellant more efficiently, allowing the separation of the heavy outboards earlier, while pumping enough propellant into the core to keep its RS-68 at 100% throttle throughout the ascent.
*Densified propellants: By adjusting the cryogenic temperatures and pressures of both the liquid oxygen and hydrogen, the propellants can be densified, allowing the loading of more propellant than standard liquid oxygen and hydrogen.
*Lighter weight: Boeing is eyeing use of large IV Heavy structures with aluminum-lithium alloys to save weight and boost performance. Replacing the current RS-68 ablative nozzle with a hydrogen regeneratively cooled one would also achieve those goals.
Boeing's Decatur, Ala., Delta IV manufacturing facility is also a cost benefit to future use of the vehicle because it is designed for high throughput and modern machining methods. The basic Delta IV Heavy price is about $200 million per vehicle, the USAF said, about half the cost of the Titan IVB it replaces.
Boeing has also looked at other IV Heavy derivatives that would cluster 5-7 common cores with 5-7 RS-68 first-stage engines for 85-metric-ton Earth orbit payloads and 36-ton capability to Mars.
And it has considered increasing the diameter of the clustered cores from 16.1 ft. to 23 ft. for more propellant, giving the vehicle a payload capability comparable to the 7.5-million-lb.-thrust Saturn V. But the concepts with the multiple or enlarged cores would require new pad infrastructure and are not likely for any near-term mission options.
Well, I think that the Delta IV Heavy is a good idea. I like the idea of evolving the vehicle in phases. Using a crossfeed system makes sense, then when the boosters are jettisoned, the core vehicle would represent a true second stage at that point. (Analyzing rockets with boosters is tricky, because the mathematics of 'staging' must be by propellant accounting as well as hardware jettisoned. This somewhat complicates things--but not too much.)
I don't mind them using solid rocket motors for strap ons, but I'd have to agree that for a man rated vehicle this isn't a good idea. Most people don't realize that a solid rocket motor is basically just a great big pipe bomb that hopefully doesn't explode! Things can happen very fast inside the high-pressure energetic environment of the combustion channel. If for instance a particularly large section of propellant comes loose and should happen to block the nozzle throat even for a millisecond, then the pressure wave caused by the motor 'blowing chunks' (please pardon the phrase, I couldn't resist!) and the cavity formed by the loss of propellant could send a sharp pressure pulse powerful enough to shear through the motor case. This will destruct the motor as quickly as if the destruct charges had been fired.
Solids are great for boosting payload, liquids are great for boosting people. I tend not to mix the two if I can help it!
Clustering the liquid boosters sounds like a tricky but doable idea. The first Saturn-1 vehicles were essentually a cluster of modified Redstone (or was it Jupiter?) missiles stuck together--they were heavily modified of course, but that was the idea. However the concept was apparently derided by some at NASA at the time who referred to the Saturn 1 as "Clusters last stand!" The concept worked, and the Saturn 1 was a success.
The Russians as I recall had an evolved version of their Energia booster in mind as well: The Energia/Vulkan which utilized a full 8 strapons instead of Energia's four. A nice rendering can be found here:
http://k26.com/buran/Info/Hercules/vulkan.html
The machine ought to have been capable of lofting something like 175 metric tons into orbit.