Falcon 1 Falcon 1e

The Falcon 1e is the upgraded version of the Falcon 1 that SpaceX announced, specified in detail and never flew. It was no vague paper project: revision 7 of the Falcon 1 user's guide, the commercial document with which the company sold the launcher to its customers, gives the 1e a section of its own, a field-by-field comparison table against the Falcon 1 and its own performance curves. For SpaceX it was not an alternative but a replacement: the guide states that the standard Falcon 1 would be available until mid-2010, and that from then on the Falcon 1e would become the vehicle for transporting small payloads.

The premise of the 1e was to make full use of the capacity and performance of an upgraded Merlin engine, and to adapt the rest of the vehicle to that power. The first stage received an extended tank to feed the higher propellant consumption and was strengthened to cope with larger axial loads. The guide puts the length of the Falcon 1e at 90 feet — about 27.4 metres — against the 70 feet (21.3 metres) it attributes to the complete Falcon 1 with fairing and interstage, while keeping the same diameter of 5.5 feet, roughly 1.68 metres.

The growth shows best in the masses. The 1e first stage went from the 3,000 pounds of Falcon 1 dry mass to 5,680 pounds (about 2,576 kg), and from 47,380 pounds of usable propellant to 87,000 pounds, around 39,464 kg. Sea-level thrust rose from 78,000 to 125,000 pounds-force, and the first stage's vacuum specific impulse improved from 300 to 304 seconds. Nominal burn time, by contrast, stayed at 169 seconds in both versions: the stage was bigger, not slower.

The fairing changed too. Against the Falcon 1's biconic aluminium skin-and-stringer fairing of 320 pounds, the 1e introduced a composite ogive one, larger and lighter — about 300 pounds — 1.7 metres in diameter and with two access doors as a standard service. It is a telling detail about the intended customer: the bottleneck of a small launcher is rarely mass, and almost always the volume available to the satellite.

The second stage was common to both versions, and the guide's table describes it only once: monocoque structure in aluminium-lithium alloy, a single pressure-fed Kestrel 2 engine with 6,900 pounds-force of vacuum thrust and 317 seconds of specific impulse, 1,200 pounds of dry mass, 8,900 pounds of usable propellant — some 4,036 kg — heated helium pressurisation, attitude control through electromechanical actuators in pitch and yaw and cold gas thrusters in roll, restart capability and a nominal burn of 418 seconds ended at a predetermined velocity. Both versions equally shared their propellants, liquid oxygen and kerosene, and stage separation by explosive bolts with pneumatic pushers.

Gunter's Space Page credits the Falcon 1e with 1,010 kg to low Earth orbit, against the 470 kg of the operational Falcon 1 configuration. The user's guide curves point the same way: they plot the performance of both vehicles, with direct insertion and with two-burn insertion, for altitudes of 185, 300, 500 and 700 km, and the top of the Falcon 1e scale is around 1,000 kg. The figure should be read for what it was, a commercial promise for a vehicle with no flights: the guide itself admits that the 1e mass properties were to be determined and that its layout and coordinate system drawings were "in work".

The schedule kept slipping. Revision 7 of the guide places 1e flights in the second quarter of 2010 and later; Encyclopedia Astronautica records it as an extended-tank version planned from 2010. Gunter's Space Page adds the end of the story: introduction was postponed until at least 2012 because of the higher priority of the Falcon 9, and its list of planned Falcon 1e launches is empty. SpaceX ended up abandoning the small payload segment to concentrate on a far larger vehicle, and the Falcon 1 was retired in 2009 after five flights without its successor ever reaching the pad.

Sources disagree about the 1e engine. The SpaceX user's guide, a manufacturer document dated 2008, designates the Merlin 1C for both the Falcon 1 and the Falcon 1e, and explains the upgrade as making full use of the capacity of an improved Merlin. Gunter's Space Page, by contrast, describes the 1e as fitted with the regeneratively cooled Merlin 1D. The difference is probably chronological — the guide is from 2008 and the entry was updated much later, once the Merlin 1D name existed — but the material consulted does not allow it to be settled, so both attributions are recorded here as their sources give them.