Universal Space Vehicle Design Concept to Defend the Earth against Asteroidal-Cometary Danger

Transcription

1 Universal Space Vehicle Design Concept to Defend the Earth against Asteroidal-Cometary Danger Abstract V.A. Volkov, V.A. Danilkin, V.G. Degtyar, G.G. Sytyi State Rocket Centre "Makeyev Design Bureau", Miass, Russia Theoretical and experimental estimations are given on the structure of a universal space interceptor designed on the modular principle. The interceptor comprising one command-impact module and a variable number of separable impact modules, each with propulsion and guidance systems, can be injected into a trajectory towards an Earth approaching space object by launch vehicles MOLNIYA, PROTON, TITAN-4, ARIANE-5, N-2, and ANGARA. The universal space interceptor is capable to attack Earth approaching asteroids and comets of up to 300 m in diameter and destroy them into a number of safe fragments. In this case objects with a diameter of up to m are destroyed by non-nuclear kinetic module and to attack larger objects it is required to use a nuclear explosive device. Introduction In recent years scientific and technical specialists of a number of advanced countries have been actively considering a problem of the development of an Earth asteroid-comet protection system. The conceptual research works show that it is possible to start developing such system in the near future on the basis of the experience in the field of space-rocket technologies with existing monitoring means and launch vehicles. The space-rocket interceptor characteristics significantly depend on the purpose, type and power of dangerous space objects (DSO) attack means, launch vehicle capability and characteristics of the existing DSO detection facilities. In the reference papers [1, 2] the possibility of pre-detected DSO trajectory deviation with nuclear and non-nuclear attack means is described. The paper discusses the development of a space vehicle to intercept Earth approaching DSO up to 300 m in diameter. As the range of such DSO detection is too short their trajectory deviation is not possible and they must be disintegrated into small fragments. Operating conditions for close-range Earth protection system Purpose Asteroids, comets and fragments are considered here as interception objects crossing an Earth orbit, which may cause their impact on the Earth. In Figure 1 the frequency of various-diameter DSO impacts on the Earth is presented. The curve is plotted from the formula

2 F (D) = 1530 D - 2.8, where F (D) is a stream of objects (1 per year) larger than D (m) [1]. The Figure 1 analysis shows that usually space objects of up to 100 m fall on the Earth once per several centuries and those of more than 200 m, once within millennium. Smaller space objects fall on the Earth more often. Not all the objects in the Earth atmosphere are dangerous. According to [3] the bodies of 1-3 m are fully decelerated by the atmosphere and a m object, like Tunguska meteorite, can ruin a large city. Thus, the minimum size of a dangerous space object is considered to be about 20 m (such object s kinetic energy is about a megaton of trotyl). In Table 1 an expected number of various-size DSO - Earth collisions during 20 years is given. Figure 1: Number of DSO-Earth impacts versus DSO diameter DSO diameter, m more than 300 Expected number of DSO (3-4) 10-3 Table 1: Expected number of DSO - Earth impacts during 20 years The analysis of Table 1 figures shows that the statistic probability of larger than 300 m DSO-Earth impacts is insignificant. DSO detection facilities At present astronomers generally use optical and radio telescopes (radars). The DSO detection range depends on a number of parameters: DSO dimensions, material and surface structure, DSO sight line position relative to the Sun detection, characteristics of the detection facilities used. In Figure 2 there is shown the maximal range of DSO detection with radars (radar stations) GOLDSTONE and EVPATORIYA and optical telescopes of 0,6-2 m in diameter. The asteroid phase is accepted to be full Moon, albedo 0,1 [4]. As Figure 2 shows, optical telescopes make it possible to detect DSO million kilometres distant from the Earth (DSO diameter is m) and to roughly

3 estimate their trajectories. When DSO is million kilometres from the Earth radar stations may be used to determine the trajectories within the accuracy required. Figure 2: Maximum range of asteroid detection with optical telescopes and radar stations DSO attack means A dangerous space object must be either shifted from its trajectory or disintegrated into small fragments. DSO of m can be detected about hours before its approach to the Earth (when DSO-to-Earth approach velocity is within 70 km/s). During this time an interceptor starts at 11 km/s initial velocity, reaches km altitude and attacks DSO s before its collision with the Earth. In this case about km/s additional velocity is required to be imparted to DSO to deflect it from the trajectory by about km (slightly more than the Earth radius). However, it is shown in [1, 2] that it is not possible to impart DSO more than 1-10 m/s incremental velocity without its disintegration. So, when intercepting DSO of less than 100 m the only way to eliminate dangerous effects on ground objects is to destroy DSO into small fragments (no larger than 1-3 m). It is shown in [1] that DSOs can be destroyed with kinetic star-shaped penetrators (KSP). A set of several KSPs (total mass of up to 10 tons, impact speed - 30 km/s) is required to destroy DSO of m in diameter. As present-day launch vehicles cannot launch payloads heavier than tons, to destroy larger DSO it is required to use more powerful and compact, in comparison with KSP, attack means, e.g. nuclear explosive devices (NED). In Table 2 there are given the estimates of NED power required to destroy stony DSO with contact exploding [5].

4 DSO diameter, m NED power, kt NED mass, kg , ,380 1,127 Table 2: Nuclear charge power required By comparison with NED, KSP is capable to disintegrate DSO with considerably lower power consumption. By estimate [5], in contact NED exploding only about 10% of explosion energy penetrates DSO and the rest 90% is scattered in space. Most of the depth energy is spent for DSO material heating: about 0.1 % of DSO mass evaporates, 1% - melts and within 3-7% is thermally damaged. The explosion seismic wave is formed with just 1% of full explosion energy. On KSP impact and deep penetration the DSO is damaged along the full length of the hole and material evaporation and plasma initiation is a minimum. As a result, the impact energy is almost completely spent for DSO disintegration. Due to the above features the KSP efficiency is by more than two order higher than that of NED (thus, either 140 ktpower NED or 1 kt-power KSP is required to disintegrate DSO of 100 m in diameter). DSO interception altitude. Launcher power required To eliminate the threat of large DSO impact on the Earth it is necessary not only to disintegrate DSO into small (1-3 m) fragments, but also to provide an average distance between them of no less than 10 times as large as their diameter during their atmosphere entry [1, 3]. In Table 3 an altitude required for KSP - DSO interception is given as a function of the DSO diameter. 1% of full KSP impact energy (KSP mass is 6 tons) is accepted to be spent for DSO fragments separation (DSO material density is 2000 kg/m 3 ). In the same Table there are given also interceptor s initial velocity at a 200 km altitude required for the interceptor to fly along a semielliptical trajectory to the point of its impact with DSO at an altitude specified and interceptor s flight duration. In this case the flight duration includes the time of interceptor injection into a 200 km reference orbit, interceptor flight along the reference orbit from the orbit injection point to that of transfer to the DSO DSO diameter, m Minimum DSO interception Initial speed, km/s altitude, thou. Km < Table 3: DSO interception altitude required Duration of flight, hour

5 interception trajectory (1.47 hour per circuit), interceptor flight along a semielliptical trajectory to the point of impact with DSO. The Table 3 data indicate that DSO of up to 150 m in diameter may by intercepted by KSP at an km altitude. In this case the interceptor initial velocity is within km/s, flight duration does not exceed a day. Interceptor launch means To intercept DSO a space interceptor comprising a set of KSPs several tons by mass, DSO guidance and trajectory correction equipment must be injected into DSO impact trajectory (initial velocity up to km/s) by launch means (launch vehicle and post boost stage). A nuclear explosive device of up to kg may be required to be launched instead of a set of KSPs. In Table 4 and Fig.3 there are characteristics of some appropriate Russian launch vehicles (LV). Besides Russian LVs foreign launch vehicles such as ATLAS, TITAN-3, TITAN-4, ARIANE-4, N-2 and others, which have similar characteristics, may be used to launch space interceptors. In Table 5 basic spaceports and launch vehicles used are presented. The period of space interceptor preparation and injection into the trajectory to the point of impact with DSO is specified by the DSO detection range, DSO velocity and interception altitude. Figure 3: Initial payload boost velocity at 200 km altitude In Figure 4 there are given estimates of a minimum diameter DSO which may be intercepted at an altitude required (Table 3) at prelaunch preparation (from the moment of DSO detection to LV launch) of 18, 2 and 1 days and target and mission data specification period (from the moment of DSO detection with radar facilities to LV launch) for 6, 3 and 2 hours. Here a range of diameters and velocities of DSO to be intercepted is also given. Payload mass, t Commercial Launch Takeoff injected into boosted to Prelaunch launch cost, $ vehicle mass, t 200 km orbit km/s velocity preparation, days million PROTON * ZENIT 458 within * MOLNIYA 304 about ANGARA** 25 * With extra post boost stage ** Under development Table 4: Characteristics of some Russian launch vehicles

6 Spaceports State Orbit inclination, deg. Launch vehicles Baikonur Russian & Kazakhstan Wandenberg USA TITAN-4 Table 5: Spaceports SOYUZ-U, MOLNIYA-M, TSIKLON-2, ZENIT-2, PROTON, ROKOT, ANGARA Canaveral USA ATLAS-2M, SPACE SHUTTLE, TITAN-4 Kuru France 0 90 ARIANE-4, ARIANE-5 Plesetsk Russia SOYUZ-U, MOLNIYA-M, TSIKLON-2, ZENIT-2, ANGARA Svobodnyi Russia ROKOT, ANGARA Sichan China CZ-2E, CZ-3, CZ-3A, CZ-3B Tanegosima Japan N-2, N-2A, light-class LV Figure 4: Minimum diameter of DSO to be intercepted (T PP - prelaunch preparation period, T TMD -target and mission data specification period) Figure 4 shows that an LV prelaunch preparation period of days (Table 4) eliminated the possibility of interception of a number of DSOs considered to be objects-targets for a close-range interception complex. When target and mission data specification lasts for 6 hours small (20-50 m-diameter) high-velocity (40-72 km/s) DSOs cannot be intercepted. To intercept any-size DSO approaching the Earth at any velocity within 72 km/s the prelaunch procedures are required to be no longer than 1-2 days. In this case target and mission data must be specified within 2-3 hours. Universal space interceptor A space interceptor designed to intercept Earth approaching DSOs must meet the requirements: - DSO attack means:

7 - a set of several KSPs each guided on an aiming point to not lower than 20 m accuracy (standard deviation (SD)); - a single KSP of up to 1 t targeted into the centre of DSO to not lower than 10 m (SD) accuracy; - a nuclear explosive device up to 1127 kg directed to DSO to not lower than 50 m accuracy (SD); - interception altitude - within km; - independent flight period - within 24 hours; - space interceptor should be launched with various-payload capacity launch vehicles. All the above requirements are considered to be satisfied with various completeness of the same universal space interceptor (USI) designed on the modular principle. USI comprises a command-impact module (CIM) with an USI control system, a system for DSO long-range detection, final inspection and calculation of KSP aiming points, telemetry and radio command communication systems, propulsion system for flight trajectory correction and direction of other USI modules to the aiming points specified and a various number of impact modules (IM) with DSO self-guidance equipment, close-range observation means, propulsion system for flight trajectory correction. In Table 6 each command-impact and impact module subsystem mass is presented. Item CIM IM Star-shaped penetrator Control equipment Propulsion system (dry) Structure Total mass without fuel and explosive device Table 6: MSI modules mass distribution (kg) On estimation of USI fuel required the USI-DSO delivery accuracy was accepted to be within 25 km (3 SD) at an interception altitude of km, USI-DSO approach velocity-70 km/s, USI-DSO guidance accuracy specified as deviation of USI-DSO approach velocity vector from DSO direction not lower than radian (3 SD) provided that precise orientation celestial sensors are used aboard CIM and IM selfguidance accuracy - not lower than radian (without sensors), specific impulse of correcting propulsion systems m/s, 20-m DSO detection range no less than km. A DSO hit accuracy required can be achieved during final correction of the CIM (IM) trajectory within 20 km from DSO. Thus, it is accepted that by the moment of DSO approach the distance between USI modules must be no less than 25 km to eliminate the preceding module engines interference in CIM (IM) to - DSO targeting during final trajectory correction. In Table 7 the estimates on the CIM fuel capacity required are given. The following manoeuvres are performed after DSO detection with CIM on-board equipment: - USI trajectory correction with celestial sensors (manoeuvre 1);

8 - successive IM separation (manoeuvres N, where N is a number of separable IMs); - CIM trajectory correction with celestial sensors (manoeuvre 3); - CIM (IM) to-dso self-guidance (manoeuvre 4). In view of orientation and stabilization the fuel consumption per each manoeuvre is increased by 5%. The Table 7 analysis shows that to support all CIM manoeuvres kg fuel is enough (minimum - for a single CIM, maximum - for 5 IM-interceptor). 225 kg of fuel (2700 m/s specific impulse) is required for IM self- guidance at 6300 m initial guidance error, 20 m guidance accuracy and radian velocity vector control accuracy. Manoeuvre No Time (period) before DSO impact, s Distance to DSO, thou. Km Error of DSO impact after manoeuvre, m Correction pulse required, m/s Manoeuvre starting mass, kg Fuel consumption, kg USI-6* USI-5* USI-3* USI-1** USI-N*** *USI comprising 6, 5 or 3 modules **USI as a single CIM ***USI comprising CIM with nuclear explosive device Table 7: Fuel consumption in manoeuvring Total fuel consumption, kg

9 1 - steering engine 7 - USI trajectory correction engine 2 - instrumentation bay 8 - command gyro instruments 3 - CIM trajectory correction engine with celestial sensor 4 - kinetic star-shaped penetrator 9 - optical system 5 - fuel supply system 10 - telemetry equipment 6 - fuel tanks 11 - explosive device volume Figure 5: Command-impact module layout 1 - steering engine 2 - kinetic star-shaped penetrator 3 - self-guidance equipment container 4 - correction engine Figure 6: Impact module layout 5 - explosive device volume 6 - fuel supply system 7 - fuel tanks Figure 3 and Table 7 show that due to various completeness USI may be launched by LV MOLNIYA (USI-1 and USI-N), ZENIT (USI-3), PROTON (USI-5) to altitudes within km. USI-6 may be launched with LV ANGARA. In Figure 5 a command-impact module layout is given. The module length is 2.3 m, diameter m, mass kg, fuel capacity - within 600 kg. In Figure 6 an impact module

10 layout is given. The module length is 1.5 m, diameter - 3.0, total mass kg (225 kg fuel capacity). The IM-DSO impact efficiency is increased with an explosive device. In this case a cumulative explosive device is considered to be more efficient, which, exploded at about 1 m from DSO surface, damages the DSO surface layer and makes it possible to increase the depth of KSP DSO penetration. An explosive device may become necessary to intercept large-size DSO or DSO of high-strength materials (iron or stony-iron asteroids). The USI of minimum completeness comprises a single command-impact module. Depending on the purpose specified USI may comprise up to 5 impact modules, nuclear explosive device, emergency safety system (ESS). ESS is initiated in emergency during prelaunch preparation and in flight, drifts USI (whole or NED) from a dangerous area and supports its soft (parachute) touchdown. The USI components have in-line arrangement and in the atmosphere re-entry leg are protected with an aerodynamic fairing. In Figure 7 there are various-completeness USI layouts aboard high and low payload capacity launch vehicles. In Table 8 basic characteristics of various-completeness USI are given. USI-1 USI-N USI launch vehicle 2 - LV adapter 3 - USI adapter 4 - interceptor attachment 5 - command-impact module 6 - USI aerodynamic fairing 7 - nuclear explosive device 8 - emergency safety system 9 - impact module 10 - LV aerodynamic fairing Figure 7: Layouts of various-completeness USI aboard launch vehicles

11 USI completeness USI-6 USI-5 USI-3 USI-1 USI-N Number of IM USI mass, kg USI length, m USI diameter, m KSP set mass, kg NED mass, kg DSO intercepted diameter, m Launch vehicle ANGARA PROTON ZENIT MOLNIYA Note: Mass and dimension data are given for USI without adapter, aerodynamic fairing and safety support system. USI operation procedure Table 8: USI basic characteristics On detection of an Earth approaching DSO ground data support facilities (first optical then radio telescopes) determine (adjust) its flight trajectory, size and class. In terms of the DSO-Earth impact point predicted and possible after-effects the necessity of DSO interception is determined and the DSO interception point and USI completeness are specified. After this the launch complex, launch vehicle, post boost stage and USI prelaunch preparation is performed, LV is launched and USI is injected into a trajectory to the USI-DSO impact point. The prelaunch procedures duration is minimized since the interception complex is kept on the alert. During USI independent radio-controlled flight the necessary USI trajectory adjustment is made. On DSO detection with USI on-board equipment the USI flight trajectory is adjusted (about 1000 s before impact). Impact modules are separated one-by-one (within every 100 s) and deployed as a sequence of modules at intervals of about 25 km. The command-impact module is behind the chain of impact modules. On the basis of DSO final inspection with CIM on-board facilities the most appropriate KSP-DSO surface impact points are specified. At km from DSO the impact modules self-guidance onto the points specified is performed. On the basis of IM-DSO impact monitoring and prediction of its own DSO impact accuracy the command-impact module generates a message on the successful DSO interception. Ground monitoring facilities confirm DSO disintegration into fragments and estimate the trajectories of the largest ones to make it possible to qualify the DSO material, structure and mechanical properties (predetermined by the remote monitoring data). Conclusions 1. By the analysis of the possible frequency of various-size space objects falls on the Earth there are distinguished objects of m in diameter the probability of

12 collision with which is relatively high (several collisions during 20 years are possible), but which cannot be predetected with present-day monitoring facilities. Such DSO may be intercepted at an altitude within km with either a set of kinetic star-shaped penetrators (DSO diameter within m) or a nuclear explosive device. In this case the interception complex must be always kept in operational conditions (prelaunch preparation lasts for about 1-2 days after DSO is detected). 2. A concept of a universal space interceptor designed on the modular principle is proposed. The universal space interceptor comprises a command-impact module and a variable number (from 0 to 5) of impact modules. Each module is provided with a kinetic star-shaped penetrator and DSO guidance system. In this case DSO long-range detection and final inspection, determination of appropriate DSO surface impact point, USI trajectory adjustment (in independent flight), USI separation to modules, module-to-dso approach arrangement required and USIground services communication is supported with the command-impact module systems. 3. The characteristics of present-day launch vehicles of different payload capacity (MOLNIYA, ZENIT, PROTON, ANGARA, et al.) and space monitoring facilities are sufficient to provide USI efficient application. 4. In the course of the universal space interceptor development the basic issues which arise during creation and operation of a dangerous space object protection system will be theoretically substantiated and tested. References [1] Alekseev A.S., Vedernikov Yu.A., Velichko I.I., Volkov V.A. The Rocket Conception of Cumulative Impact Defence of the Earth Against Dangerous Space Objects. Impact Engineering, # 1-5, pp.1-12, [2] Velichko I.I., Volkov V.A., Tambulov N.F. The rocket conception of the Earth protection against asteroids and comets. A report made at the International Conference The problems of the Earth protection against dangerous space objects (SPE-94), Snezhinsk, [3] Tikhonov N.N. The research of the space body-earth atmosphere interaction. A report made at the International Conference The problems of the Earth protection against dangerous space objects (SPE-94), Snezhinsk, [4] Kuriksha A.A. The possibilities of the Earth approaching asteroids detection and tracking, Konversiya v mashinostroyenii, #1, [5] Iljin V.V., Rudin V.N. The issues of interceptor dangerous space object approach and impact conditions. A report made at the International Conference The problems of the Earth protection against dangerous space objects (SPE-94), Snezhinsk, [6] Volkov V.A., Degtyar V.G., Mogilenko V.I., Sytyi G.G. A Universal Space Vehicle To Defend The Earth Against Asteroidal-Cometary Danger, IAA-01- C.2.06, Toulouse, France, 2001.