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A low-tech health monitor for the solar-photon sail
Acta Astronautica 60 (2007) 55 – 56 www.elsevier.com/locate/actaastro
Academy transactions note
A low-tech health monitor for the solar-photon sail Gregory L. Matloffa, b,∗ , Lufeng Lenga a Department of Physics, New York City College of Technology, 300 Jay Street, Brooklyn, NY 11201, USA b IAA Section 2 (Engineering Sciences), USA
Received 4 July 2006 Available online 20 September 2006
Abstract On-orbit deployment tests and operational missions for first-generation solar-photon sails may require a method of monitoring post-deployment sail health. A low-technology device capable of performing this function is the pinhole camera, combined with an inflatable hydrostatic beam mounted at the sail’s center of mass. © 2006 Elsevier Ltd. All rights reserved.
1. Introduction During a joint physics–math colloquium at our institution in late 2005, Les Johnson of the NASA Marshall Space Flight Center discussed the current state of NASA solar-photon-sail development efforts. One current aspect of this research is the investigation of techniques to monitor the post-deployment condition or “health” of a first-generation Earth-launched solar photon sail. Although solution to this problem seems conceptually simple, it is more subtle than immediately apparent. A sail health-monitor must be permanently stationed near a large, gossamer sail under constant acceleration. It must be low mass and capable of delivering highresolution information to the craft’s on-board computer. A tether-mounted system may not be stable in the case of a slowly spinning disc sail. In addition, the system must be of high reliability and capable of functioning for
∗ Corresponding author. Department of Physics, New York City College of Technology, 300 Jay Street, Brooklyn, NY 11201, USA. Corresponding Member, IAA Section 2 (Engineering Sciences). E-mail address: [email protected] (G.L. Matloff).
0094-5765/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.actaastro.2006.08.001
months or longer in the inner-solar-system interplanetary environment without interfering with sail function. 2. The Pinhole Camera One device capable of performing this function is the Pinhole Camera [1]. Fig. 1 demonstrates operation of this device, which may be the simplest imaging apparatus. Light enters the camera box through as small an aperture as possible and falls on a surface interior to the camera. If the image linear dimension is called IMAGE, the sail diameter is DIAMsail , the distance between the sail and camera box is DISsail , and the camera length (from pinhole to image plane) is Lcam , elementary geometry allows us to immediately write DIAMsail /DISsail = IMAGE/Lcam .
(1)
Assume, for example, that DIAMsail = DISsail = 50 m and that IMAGE=Lcam =1 cm. If the image falls against the lens of a digital camera with 1000 pixel×1000 pixel resolution (not unusual for modern digital cameras integrated with cellular phones), each pixel corresponds to a sail segment with dimension 5 cm.
56
G.L. Matloff, L. Leng / Acta Astronautica 60 (2007) 55 – 56
Sail camera
Image
DIAMsail DISsail Lcam
Fig. 1. The Pinhole Camera used to image a solar photon sail. All symbols are defined in text.
inflatable boom near the sail’s centerline. Camera-box stability would be improved by coating it with a lowreflectance layer facing the Sun. But this strategy would increase camera-component temperature. 4. Conclusions
Pre-camera deployment
Post-camera deployment
Sunlight direction
Fig. 2. Camera is deployed using an inflatable boom.
As discussed in the next section, the sail and camera box could be attached using an inflatable boom mounted to the sail center of mass, on the sunward side of the sail. Two to four digital cameras could be mounted around the boom within the camera box, so that the boom would not overly interfere with the sail image. A few colorcoded 10-cm telltales on various portions of the sail could be used to allow easy discrimination of various sail sections without measurably reducing sail performance. Digital images could be “e-mailed” to the main spacecraft computer using modifications of technology integral to modern cellular phones. 3. The hydrostatic inflatable boom One method of attaching the camera box to the sail is to utilize a hydrostatic inflatable boom, as demonstrated in Fig. 2. Such a device would be extended to full length and inflated by pressurized gas after sail unfurlment. As discussed by Genta and Brisca, the mass of such a boom would be less than a kilogram, if its length were 50 m, and its diameter were 0.36 cm [2]. Since the sail is accelerating under the influence of solar radiation pressure, inertia will tend to maintain the
The total mass of a millimeter-thin camera box with dimensions of a few centimeters, one-to-four cellularphone-sized digital cameras, the inflatable boom, and associated electronics would certainly not exceed a few kilograms. The physical projected area of the camera box will be much less than 1% of the sail area. The solar-photon sail is a low-thrust space propulsion system so maneuvers will tend to be slow and gradual, unless a sundiver maneuver is performed. Therefore, a station-keeping thruster mounted on the camera box is probably not necessary. But even if a small thruster is included, the camera box will have a mass less than 1% of an first-generation, 50-m diameter sailcraft with a mass of perhaps 300 kg. Since the physical size of the camera box is so much less than that of the sail, sail performance should not be impaired by incorporation of this device. Acknowledgments We are grateful for discussions of this concept with Les Johnson and Edward Montgomery IV, both of whom are affiliated with the NASA Marshall Space Flight Center in Huntsville, Alabama. References [1] J.R. Meyer-Arendt, Introduction to Classical and Modern Optics, fourth ed., Prentice-Hall, New York, 1995. [2] G. Genta, E. Brusca, The parachute sail with hydrostatic beam: a new concept for solar sailing, Acta Astronautica 44 (1999) 141–146.
Academy transactions note
A low-tech health monitor for the solar-photon sail Gregory L. Matloffa, b,∗ , Lufeng Lenga a Department of Physics, New York City College of Technology, 300 Jay Street, Brooklyn, NY 11201, USA b IAA Section 2 (Engineering Sciences), USA
Received 4 July 2006 Available online 20 September 2006
Abstract On-orbit deployment tests and operational missions for first-generation solar-photon sails may require a method of monitoring post-deployment sail health. A low-technology device capable of performing this function is the pinhole camera, combined with an inflatable hydrostatic beam mounted at the sail’s center of mass. © 2006 Elsevier Ltd. All rights reserved.
1. Introduction During a joint physics–math colloquium at our institution in late 2005, Les Johnson of the NASA Marshall Space Flight Center discussed the current state of NASA solar-photon-sail development efforts. One current aspect of this research is the investigation of techniques to monitor the post-deployment condition or “health” of a first-generation Earth-launched solar photon sail. Although solution to this problem seems conceptually simple, it is more subtle than immediately apparent. A sail health-monitor must be permanently stationed near a large, gossamer sail under constant acceleration. It must be low mass and capable of delivering highresolution information to the craft’s on-board computer. A tether-mounted system may not be stable in the case of a slowly spinning disc sail. In addition, the system must be of high reliability and capable of functioning for
∗ Corresponding author. Department of Physics, New York City College of Technology, 300 Jay Street, Brooklyn, NY 11201, USA. Corresponding Member, IAA Section 2 (Engineering Sciences). E-mail address: [email protected] (G.L. Matloff).
0094-5765/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.actaastro.2006.08.001
months or longer in the inner-solar-system interplanetary environment without interfering with sail function. 2. The Pinhole Camera One device capable of performing this function is the Pinhole Camera [1]. Fig. 1 demonstrates operation of this device, which may be the simplest imaging apparatus. Light enters the camera box through as small an aperture as possible and falls on a surface interior to the camera. If the image linear dimension is called IMAGE, the sail diameter is DIAMsail , the distance between the sail and camera box is DISsail , and the camera length (from pinhole to image plane) is Lcam , elementary geometry allows us to immediately write DIAMsail /DISsail = IMAGE/Lcam .
(1)
Assume, for example, that DIAMsail = DISsail = 50 m and that IMAGE=Lcam =1 cm. If the image falls against the lens of a digital camera with 1000 pixel×1000 pixel resolution (not unusual for modern digital cameras integrated with cellular phones), each pixel corresponds to a sail segment with dimension 5 cm.
56
G.L. Matloff, L. Leng / Acta Astronautica 60 (2007) 55 – 56
Sail camera
Image
DIAMsail DISsail Lcam
Fig. 1. The Pinhole Camera used to image a solar photon sail. All symbols are defined in text.
inflatable boom near the sail’s centerline. Camera-box stability would be improved by coating it with a lowreflectance layer facing the Sun. But this strategy would increase camera-component temperature. 4. Conclusions
Pre-camera deployment
Post-camera deployment
Sunlight direction
Fig. 2. Camera is deployed using an inflatable boom.
As discussed in the next section, the sail and camera box could be attached using an inflatable boom mounted to the sail center of mass, on the sunward side of the sail. Two to four digital cameras could be mounted around the boom within the camera box, so that the boom would not overly interfere with the sail image. A few colorcoded 10-cm telltales on various portions of the sail could be used to allow easy discrimination of various sail sections without measurably reducing sail performance. Digital images could be “e-mailed” to the main spacecraft computer using modifications of technology integral to modern cellular phones. 3. The hydrostatic inflatable boom One method of attaching the camera box to the sail is to utilize a hydrostatic inflatable boom, as demonstrated in Fig. 2. Such a device would be extended to full length and inflated by pressurized gas after sail unfurlment. As discussed by Genta and Brisca, the mass of such a boom would be less than a kilogram, if its length were 50 m, and its diameter were 0.36 cm [2]. Since the sail is accelerating under the influence of solar radiation pressure, inertia will tend to maintain the
The total mass of a millimeter-thin camera box with dimensions of a few centimeters, one-to-four cellularphone-sized digital cameras, the inflatable boom, and associated electronics would certainly not exceed a few kilograms. The physical projected area of the camera box will be much less than 1% of the sail area. The solar-photon sail is a low-thrust space propulsion system so maneuvers will tend to be slow and gradual, unless a sundiver maneuver is performed. Therefore, a station-keeping thruster mounted on the camera box is probably not necessary. But even if a small thruster is included, the camera box will have a mass less than 1% of an first-generation, 50-m diameter sailcraft with a mass of perhaps 300 kg. Since the physical size of the camera box is so much less than that of the sail, sail performance should not be impaired by incorporation of this device. Acknowledgments We are grateful for discussions of this concept with Les Johnson and Edward Montgomery IV, both of whom are affiliated with the NASA Marshall Space Flight Center in Huntsville, Alabama. References [1] J.R. Meyer-Arendt, Introduction to Classical and Modern Optics, fourth ed., Prentice-Hall, New York, 1995. [2] G. Genta, E. Brusca, The parachute sail with hydrostatic beam: a new concept for solar sailing, Acta Astronautica 44 (1999) 141–146.