SpaceX nearly reaches orbit with Starship-Superheavy

Starship launches from Boca Chica as Superheavy’s exhaust engulfs the pad, 14 Mar 2024. (NSF)

SpaceX launched Integrated Flight Test 3 from Boca Chica on 14 March 2024 1325 UTC in a major test of the Starship-Superheavy launch system. The suborbital flight flew farther than ever before, and technically was within reach of, but did not get to, orbit. Even after a hot fire separation and “orbital insertion burn,” Starship’s trajectory was suborbital. But given the other issues faced in the flight, it was probably the right call to make ditching the craft the default plan.

The issue cropped up later than the last test, but still fairly early. Seven minutes in, Superheavy 10’s engines flamed out during descent and were unable to restart. Though the grid fins were able to straighten the booster as it fell, and a few engines did manage to catch flame, the planned descent profile needed several more engines (nominally, 13) to control speed for a gentle drop into the Gulf of Mexico. With the grid fins keeping it upright and 3 or 4 engines online possibly giving as much as 25% of planned thrust, Superheavy wasn’t quite in free fall, but the booster was still ordered destroyed by the range safety officer as it plunged into the sea at supersonic speed.

The final moments of Superheavy 10 as it raced toward the Gulf of Mexico at 1200 km/h (SpaceX)

The disappointment continued 45 minutes into the flight as Starship 28 took its final dive. While rolling around for reentry over the Indian Ocean, far southwest of Java and well west of Gascoyne, Western Australia, it was sailing through a squall of its own detached thermal tiles, and seemed sluggish in attempts to control yaw and roll. As it reached the atmosphere, its orientation drifted, possibly without command authority, until contact was lost 48 minutes in. Much like on the Space Shuttle, the reentry-rated thermal protection tiles are attached to one particular side of the vehicle. Unlike the Space Shuttle, Starship doesn’t have a flat surface to aim toward the reentering side, complicating kinematic control needs during this phase of flight. Clearly, tile loss is at least as fatal for Starship as it was for the Space Shuttle.

Starship 28 starting to burn up over the southeastern Indian Ocean, 14 Mar 2024. (NSF/SpaceX)

A key concern coming out of today’s flight is Raptor’s restart performance. An operational engine system needs to reignite at least a few times in spaceflight, and SpaceX mission profiles often have several main engine burns. Today’s flight shows a less than 25% success rate for Raptor restart. Though New Glenn will do so later, Starship and Superheavy are the first spacecraft to rely on restartable methalox engines. Also unlike any other engine, fuel and oxidizer flows are independent in the Raptor. The added degree of freedom is not necessarily a benefit if the reactants become mismatched.

Overall, it is still good news for SpaceX today. But that may confuse certain observers: how can a SpaceX rocket failure be good news, while a Boeing plane failure is bad news? The answer lies in the engineering process and operational phase. While Boeing’s 737 Max and 787 aircraft are still fairly new, they have reached the operational phase and have hundreds of examples flying. When a commercial airliner reaches certification, its design risk is supposed to be retired. Instead, the world has been watching its fleet literally fly apart in recent weeks, placing passengers at risk.

SpaceX isn’t flying people on Starship yet, which is still in flight tests. From both technological and economic perspectives, the success demonstrated today only needed to be incremental. Not exploding during ascent or separation, then flying 20 000 km, is indeed better than the December mission, even if there are still some very significant things that the Starship system should be able to do, but cannot. From a regulatory perspective, SpaceX needed to do far less: simply plan a mission where the worst the rocket could do was explode over the ocean. In that, IFT-3 was a complete success.

Robbie Lunnie briefs Fly-ND 2024 on Advanced Air Mobility

In 1985, Steve Meretzky at the game studio Infocom imagined the futuristic metropolis of Rockvil, South Dakota, at the centre of “The Quad-State Region” – a sprawling urbanization throughout North and South Dakota, Montana, and Wyoming, all connected by “skycars”. Though “A Mind Forever Voyaging” may remain in the realm of fiction, by the real year 2031, it may indeed be possible to fly from Bismarck to Belle Fourche in a personal eVTOL aircraft.

UND Associate Professor Robbie Lunnie shares the FAA EB-105 recommendations for Vertiport landing zones at the 2024 Fly-ND Conference on March 5. (Fargo Orbit)

The dream of the flying car has also been a powerful inspiration for Robbie Lunnie, an associate professor at the University of North Dakota School of Aerospace Sciences, who briefed the 2024 Fly-ND conference on plans for Advanced Air Mobility (AAM) and Urban Air Mobility (UAM).

Advanced Air Mobility is a coalescing set of operating principles to handle the coming wave of what could be glibly called human-sized drones. The development of high-powered lithium ion batteries, lightweight electric motors, and advanced control software that enabled the quadcopter RC revolution a decade ago has finally resulted in several viable machines, some of which may be FAA certified as early as 2025.

Expecting another wave of low-skilled users to the national airspace, NASA and the FAA have scrambled to get ahead of the problem, developing standards for AAM operations and facilities, and intentionally separating the coming traffic from existing heliports, which are mainly equipped only for professional pilots and gas-guzzling motors, instead focusing on developing new “vertiports” more properly equipped to recharge electric aircraft and handle passengers.

AAM will first be tested in rural locations like North Dakota – the wide open spaces, existing UAV testing environments, and the presence of one of the world’s largest aeronautical educational facilities, would seem to make the region a nearly perfect proving ground for new aviation concepts. Lunnie has already sketched out where one Vertiport may go – adjacent to the Fargo Aero Center at Hector International Airport, already a common transit point for Air Taxi clients. Another potential location? As close as possible to Lunnie’s own home in Thompson.

The familiar “H” at heliports may not make it to Vertiports, which may use a distinctive landing zone reticule instead. (FAA)

Urban Air Mobility applies AAM principles to the crowded space in and above cities. The dense traffic and limited available land means that uses may encounter a variety of access points, like small “Vertistops” and larger “Vertistations”, with aircraft moving along designated Urban Air Corridors. These corridors will be specially defined streets in the local airspace, which will be laid out in cityscale AFR (Automated Flight Rules) maps much like the familiar but longer-range VFR sectional charts of today. These streets in the sky will be at different altitudes based on direction of travel and whether passing is needed – and as AAM/UAM has developed, their planned altitude has risen from about FL015 in early concepts to around FL050 now. More space to work with means more safety margin in flight.

If that sounds like you’re going to need a pilot to figure it all out, you’d be right. Even though AAM/UAM expects a great deal of computerized assistance for passengers, as the first models are starting out, your eChopper will come with an onboard pilot. That could change later on, but not because of AI. Aviation has tons of existing infrastructure and uses in America, and there will always be a lot of problems to navigate around. Autonomous systems can only go so far, so the real future of “driverless” eVTOL is Turking. Much like the luxury “self driving” cars of today, a gaggle of telepresent pilots at the far end of the cellular network will be standing by to handle your takeoffs and landings. Eventually, centralized control centres could see as many as 5 flights monitored by a single certified pilot, pending the results of time and attention studies being conducted by UND and other researchers. In such a future, pilots wouldn’t be obsolete, but the offered jobs may lack the thrill of skyward motion.

Finally, how to power it all? The electrical demand from Vertiports may prove to be a unique challenge even greater than the EV revolution, if fast-charging of fixed batteries is relied on. Alternatives like drop-and-swap battery switching have also been floated, but Lunnie doesn’t think such swaps will be a feature of approved aircraft because of how the FAA regards safety matters. Presently, battery servicing is a job for certified mechanic. Landing on a spare battery could also cause a fire, so the draft EB-105 vertiport standard presently does not allow for padside storage of battery packs. Other energy sources are left entirely to future consideration.

There are still a lot of rough edges mixed with “gee-whiz” hype in the AAM/UAM mindspace. In practice, the economics may prove unfavourable in many ways, particularly when considering rural distances and load factors for AAM testing, then proceeding to the conflicting land use priorities and noise abatement measures sure to cross paths with UAM. Still, democratized flight accessible from the next street corner over is the sort of 21st Century amenity we’ve always hoped would arrive.

Stuck: UND can’t fly on UL94 until Lycoming resolves engine valve issue

UND mechanics present their results to the Fly-ND conference, 4 Mar 2024 (Fargo Orbit)

The University of North Dakota’s School of Aerospace Sciences confirmed it is continuing a pause in its switch to UL94, an unleaded avgas likely to replace 100LL, a legacy fuel with 2.2 grams of lead per gallon. The EPA and FAA are engaged in overlapping but separate efforts to eliminate leaded avgas over the next few years.

At EAA AirVenture 2023, UND announced a pioneering effort to use UL94 for its entire fleet of training aircraft. The school eventually plans to return to unleaded, but encountered teething issues, and is now waiting for a fix from engine maker Lycoming.

The results were promising at first. The University’s Piper PA28 Archers came into the repair shop running cleaner and their engines were easier for mechanics to take apart and repair. But then, after a fleet average of 450 power-on hours, their Lycoming IO-360 engines began to suffer from valve malfunctions.

The valve problems were generally irreparable except by swapping out the entire cylinder, quickly becoming a headache even with a fully staffed maintenance hangar. In a fleet that flies thousands of hours a week, the failures just kept coming at a concerning rate. UND’s mechanics ran though 120 replacement cylinders in just 4 months between June and October 2023, leaving only 60 in stock for the rest of the training year.

At present, UND’s mechanics lack a consistent theory for the failures. They briefly investigated fuel logistics as a factor, because other aircraft, like the American Champion Decathalon or the Robinson R44 helicopter, had similar engines but were still flying fine. Those aircraft mostly stick around Grand Forks, but the Archer, on the other hand, is frequently flown “cross-country” to other airports. Because 94UL was only available in Grand Forks, the planes often return filled with 100LL from another airport. But looking into this didn’t end up proving any strong link between switching fuel and the valve problems. Instead, it seemed more like planes that used more 100LL failed less.

Lastly, there were the economics of burning thousands of gallons of fuel. Though both fuels were comparable in price when UND made its decision, soon afterward, the price of 100LL dropped significantly, while UL94 stayed over $6.00 per gallon. UND Aerospace had promised students that the UL94 initiative would not be significantly expensive, yet was quickly forced to pass on relatively higher costs.

94 mogas for avgas prices in Grand Forks

Though a plane can fly with a stuck valve, it isn’t airworthy in the full meaning of the term. Placing the change on hold, the Dean of Aerospace announced a move back to 100LL. Just like the switch to UL94, the fuel systems at GFK needed no modifications, only a few decals changed at the fuelling tanks and trucks. The remaining UL94 in planes was used normally, but new fuel loads used 100LL. The switch took just 4 days.

It seems clear that Lycoming will need to isolate the issue, and respond with a fix, whether that is some list of operational changes, or a physical fix to the valve design. The issues identified by the UND effort should go a long way toward finding the right answer as quickly as possible.