The Spiral seems to be one of the most ambitious and secret projects in the
history of Soviet aviation. Therefore, only 40 years later it became possible to
disclose the whole truth of this aircraft...
Under the five-year plan of the Air Force on orbital and hypersonic aircraft,
go-ahead to actually proceed with development of a manned orbital vehicle in the
USSR was given in 1965 to the Artem Mikoyan's OKB-155 design bureau, and
55-year-old Chief Designer Gleb Lozino-Lozinsky was selected as project manager.
The new project dubbed Spiral.
The aerospaceplane project dated 29 June 1966 provided for the development of a
115-t orbital system consisting of three winged VTOL reusable aircraft: the 52-t
HLA reusable hypersonic air-breathing launch aircraft, designated '50-50'; the
RB expendable two stage rocket booster; and the OS manned orbital aerospaceplane,
designated '50'. The system would take off vertically from a launch cart at a
takeoff speed of 380-400 km/h.
The launch aircraft would accelerate the whole system to a hypersonic speed of M=6
(about 1,800 metres per second), releasing the components at an altitude of
28-30 km. The launch aircraft would return to its launch base after completing
the mission, and the booster, burning fluorine+hydrogen fuel, would propel the
aerospaceplane to the orbit.
The orbital aircraft would bring a payload of up to 10.3 tonnes to the
circumpolar orbit of 130-150 km at the carrier offset of up to 750 km, if
boosted by a launch aircraft with liquid hydrogen power plant, or 5 tonnes if
the launch aircraft burnt kerosene.
The manned reusable single-seated orbital aircraft would be employed in daytime
photographic reconnaissance, radar reconnaissance, space targets interception or
ground attack, equipped with a space-surface missile for the latter function.
The aircraft weighed 8.8 tonnes in all configurations, carrying 500 kg of combat
payload for reconnaissance and interception, and 2,000 kg in attack
configuration. Launched from the territory of the USSR, the aircraft would reach
the 130-150-km orbits, inclined by 45-135 degrees. Manoeuvrability
characteristics of the aircraft, propelled by the rocket booster power plant,
burning fluorine and amidol provided for variable orbit inclination (to allow
second target run) by 17 degrees for the reconnaissance and interception
aircraft, and 7-8 degrees for an attack aerospaceplane armed with a missile. The
interceptor version would perform a combined manoeuvre of simultaneously
changing the inclination and ascending to 1,000 km, after which it would lose
the weight to 4,900 kg.
To complete the flight, the pilot would start braking engines and the orbital
aircraft would dive into the atmosphere at a large angle of attack, its roll
deflecting from 0 to 60 deg. at stable angle of attack to control the aircraft
on descent. It would be able of performing an aerodynamic manoeuvre at gliding
trajectory within the range of 4,000-6,000 km and side deviation of 1,500 km.
The aircraft would be guided to the landing area controlling the speed vector
along the runway, which was achieved through the use of the roll programme. The
agility of the aircraft would allow it to land at a speed of less than 250 km/h
at night and in adverse weather at one of reserve 2nd class airfields in the
USSR from any of its three orbit circuits, for which the RD36-35 kerosene-fuel
turbojet engine of the Rybinsk-based OKB-36 design bureau (Chief Designer Pyotr
Kolesov) would be used.
HLA
DIMENSIONS |
Fuselage length, m |
38.0 |
Wingspan, m |
16.5 |
Wing area, sq.m |
240.0 |
Wing section, at board/at tips |
0.025/0.03 |
Elevon area, sq.m |
24.0 |
Wing aspect ratio |
1.14 |
Forward edge sweep angle, degrees |
80/60 |
Fuselage diameter (max), m |
4.15 |
Middle section |
|
(incl. wing and engine nacelles), sq.m |
20.9 |
Fuselage width (in engine nacelles), m |
6.2 |
Winglet area, sq.m |
2x18.5 |
Ventral fin area, sq.m |
10.0 |
The hypersonic launch aircraft had a layout of a large arrow-shaped variable
flying wing, with vertical stabilisers mounted at the wingtips. The wing is made
of double-wedge profile section featuring variable thickness ratio.
HLA control surfaces included rudders of the fins, elevons and landing flaps. To
improve its yaw stability, the tail unit incorporated a ventral fin, folding at
take-off. The aircraft featured a two ejection seat insulated cockpit, its nose
declining 5 degrees forward at landing to allow better field of view.
Liquid hydrogen was used as propellant for the launch aircraft. The power plant
included a set of four AL-51 turbojet engines boasting 17.5 tonnes of thrust
each designed by Arkhip Lyulka's OKB-165. They had a single air intake and a
single supersonic divergent nozzle.
With the empty weight of 36,000 kg, the launch aircraft could carry up to 16,000
kg of liquid hydrogen in tanks of 260 m3 each.
The engines' peculiarity consisted in the use of hydrogen vapours to gear the
turbine that rotated the turbojet compressor. Hydrogen evaporator was placed at
the compressor inlet. This is the way the powerplant for the aircraft was
elaborated without combining turbofan, hypersonic and turbojet engines.
The adjustable hypersonic air intake was yet another advanced feature of the
launch aircraft. It used almost entirely the forward bottom surface of the wing
and the specially designed fuselage nose to compress the air.
Dedicated construction materials and heat-resistant coatings were applied to
withstand the heat barrier.
The launch aircraft might well have been used as a long-range hypersonic
strategic reconnaissance aircraft, too. Equipped with kerosene engines, it was
expected to accelerate to M=4.0-4.5 and have a range of 6,000-7,000 km at
cruising M=4, while the hydrogen engine installed would allow it to speed up to
M=6 and cruise 12,000 km at M=5.
The OS was implanted into the launch aircraft on top, together with the rocket
booster in the shape of two-stage launch vehicle with the total length of 27.75
m (18.0 m for the first stage and the fairing and the remaining 9.75 m for the
second stage with the orbital aerospaceplane proper). The oxygen-hydrogen
booster would be a meter longer and a half-meter thicker.
The aerospaceplane itself was a flat-bottomed lifting body with a large upturned
nose. The nosecone was made as a 60-deg. segment with 1.5-m radius of the sphere.
Its design was found to greatly reduce afterbody heating during re-entry, when
it heated to 1,400 deg. Centigrade.
COMPARATIVE PERFORMANCE OF ROCKET BOOSTERS |
Versions |
main |
intermediate |
Specific pulse, s |
460 |
455 |
Length with orbital spacecraft (OS) and fairing, m |
27.75 |
28.71 |
Empty weight, t |
6.15 |
8.62 |
Takeoff weight (without OS), t |
52.7 |
51.12 |
Mixture ratio |
1:14 |
1:7.5 |
1st stage: |
|
|
empty weight, t |
5.5 |
7.7 |
fuel |
liquid Н2 |
liquid Н2 |
weight, t |
2.8 |
4,5 |
volume, cu.m |
40.0 |
60.0 |
oxidiser |
liquid F2 |
liquid O2 |
weight, t |
39.2 |
33.75 |
volume, cu.m |
25 |
30.9 |
tank diameter, m |
2.5 |
3.0 |
Takeoff weight, t |
47.5 |
45.95 |
2nd stage: |
|
|
empty weight, kg |
650 |
920 |
fuel |
liquid Н2 |
liquid Н2 |
weight, kg |
310 |
500 |
volume, cu.m |
4.42 |
6.67 |
oxidiser |
liquid F2 |
liquid O2 |
weight, kg |
4.240 |
3.750 |
volume, cu.m |
2.70 |
3.43 |
tank diameter, m |
2.5 |
3.0 |
Takeoff weight (without OS), kg |
5,200 |
5,170 |
A unique feature of the aerospaceplane was the variable dihedral wings. The
outer skin was articulated to permit thermal expansion during re-entry. The
wings were set at an angle and had a specific form, so that during re-entry at a
45-60 deg. angle of attack and the hypersonic quality of 0.8 the air stream
would flow from the body down to the wings, rather than to the wing leading
edges. Also, the wings were made separately variable to better controllability
in case of yawing.
To improve landing parameters, after becoming subsonic, dual electric actuators
moved the wings to a horizontal position, where they served as wings,
substantially increasing the lift of the aerospaceplane for airbreathing
operations, the wingspan reaching 7.4 m with a sweep of 30 deg. This increased
the aerodynamic quality to 4.5.
The 'hot structure' principle was used in ensuring heat resistant capability of
the orbital aerospaceplane. Therefore, the aircraft had a welded frame, with a
heat-resistant screen underneath, made of plates of the VN5AP clad columbium
alloy coated with molybdenum dicilicide. The plates were placed as fish scales.
The screen was attached with the help of ceramic bearings playing the part of
heat barriers, as they relieved temperature stress by means of the screen moving
relative to the body without changing the shape of the aircraft.
Landing gear normally consisted of four skids in landing gear bays mounted on
the sides of the aerospaceplane above the heat shield, and deploying in the
manner not to split the screen before landing.
ORBITAL
AEROSPACEPLANE DIMENSIONS |
Body length, m |
8.0 |
Body rear edge span, m |
4.0 |
Body front section radius, m |
1.5 |
Planform area, sq.m |
24.0 |
Body middle section, sq.m |
3.7 |
Body bottom area, sq.m |
2.8 |
Nose sweepback angle, deg. |
74.33 |
Variable wing area, sq.m |
2x33.0 |
Wing leading edge sweepback angle, deg. |
55 |
Elevon area, sq.m |
1.84 |
Fin area, sq.m |
1.7 |
Rudder area, sq.m |
0.44 |
Flap area, sq.m |
1.785 |
The power plant included:
- a liquid propellant engine (LPE) for orbital propulsion, with the 1,500 kg/f
of thrust (specific pulse of 320 sec, fuel consumption of 4.7 kg/sec). It was
employed to change orbital inclination and produce a braking pulse to dive off
the orbit. Later versions would feature a more powerful LPE with thrust in
vacuum of 5,000 kg/f, boasting a variable thrust capability, adjusting it
slightly to 1,500 kg/f to allow orbital manoeuvres;
- two emergency situation braking 16 kg/f LPEs, fed from main LPE fuel system by
the compressed helium displacer;
- an LPE attitude control unit of six 16 kg/f engines for coarse adjustment and
ten 1 kg/f engines for fine manoeuvres;
- a turbojet kerosene 2,000 kg/f engine with specific fuel consumption of 1.38
kg/kg*h to allow subsonic propulsion and landing. It had an adjustable ram air
intake at the bottom of the fin, opened only before starting the turbojet.
The first examples of combat orbital aerospaceplanes were to be equipped with
intermediate LPEs, burning fluorine-ammonia fuel.
The pilot-cosmonaut sat in an insulated 'headlight' escape capsule, equipped
with powder charges to eject the capsule at any stage of flight from taking-off
to landing. The capsule also had control engines for re-entry phase, as well as
a radio beacon, an accumulator and an emergency navigation unit. It parachuted
at a speed of 8 m/s, kinetic energy absorption effected by means of residual
deformation of the specially designed cellular structure of the capsule bottom.
The escape capsule with equipment, life-support system, escape system and the
pilot-cosmonaut weighed 930 kg, and 705 kg at landing.
The navigation and automatic control system included a self-sustained
astro-inertial navigation system, a digital airborne computer, LPE directional
equipment, astro-corrector, optical viewing device and radio altimeter.
Manual backup on direction signals was available to control the aerospaceplane
at descent.
Specialised equipment of the combat manned orbital aerospaceplanes in
reconnaissance and interceptor configurations was placed behind the cockpit in a
2 cu.m compartment, which was increased at the expense of the fuel compartment
to allow housing the space-surface missile in the ground-attack configuration.
Daytime photographic reconnaissance
aerospaceplane would provide detailed
intelligence on small-size land and mobile sea-surface targets, selected in
advance.
The photographic equipment ensured 1.2-m resolution, if employed from 130 km
orbit. The pilot-cosmonaut was to detect the target and observe the terrain with
the help of the optical viewing device. The device had an adjustable reflector
to track targets from 300 km. Picture-taking would start automatically as soon
as the pilot manually coincided the optical line of sight of the photo camera
and the viewing system with the target. The pilot should have time to make
photos of 3-4 targets during one circuit.
The reconnaissance aerospaceplane would have short-wave (HF) and ultra
short-wave (UHF) radios to transmit the data to ground control centre. If
additional target run required, an automatic orbit inclination changeover was
performed at pilot's command.
The
reconnaissance version would have a distinguishing 12x1.5-m external
expendable antenna, which was expected to be effective at 20-30 m, which is
quite enough to detect aircraft carrier groups and large land installations.
The
attack orbital aerospaceplane would be used to kill sea targets. It was
expected to launch its space-surface missile over the horizon with target
designation data available from an orbital reconnaissance aerospaceplane or a
satellite. Precise coordinates of the target would be specified by the locator,
expendable after the aerospaceplane changes the orbit, as well as by its
navigation equipment.