Orbital Mass Research Articles

Lunar-Derived Propellants for Fueling Mars-Bound Spacecraft in Cis-Lunar Space

The conventional method to send payloads to Mars is by direct trans-Mars injection (TMI) from LEO. NASA is considering an alternative of fueling large Mars-bound cargo transfer vehicles in cis-lunar space with propellants derived from the Moon by in situ propellant production (ISPP) prior to trans-Mars injection from cis-lunar space. A large team of investigators developed an Evolvable Lunar Campaign (ELC) that defined its strategic objective as follows: "The ELC strategic objective is commercial mining of propellant from lunar poles where it will be transported to lunar orbit to be used by NASA to send humans to Mars." Unfortunately, sending Mars-bound vehicles to cis-lunar space prior to trans-Mars injection saves little mass in LEO, unnecessarily includes lunar ISPP, which is costly, complex, and risky, and at the bottom line, has no benefits. The problem is that the amount of propellant needed to go from LEO to cis-lunar space is roughly comparable to the amount of propellant used for direct TMI from LEO, so the lunar-derived propellants only offset a small amount of propellant used to augment Mars Orbit Insertion and Entry, Descent, and Landing, and the amount of propellant required in LEO is almost the same in both cases. The initial mass in low Earth orbit (IMLEO) is not reduced much by utilizing lunar ISPP. At the bottom line, sending Mars-bound MCTV to cis-lunar space adds complexity, cost, and risk and provides essentially no benefits.

Sparse representation for massive MIMO satellite channel based on joint dictionary learning

AbstractA constrained joint dictionary learning (CJDL) algorithm for high‐precision channel representation in massive multiple input multiple output (MIMO) satellite systems is proposed. Furthermore, taking into account the angular reciprocity of massive MIMO satellite systems, joint dictionary learning can establish a common support basis for both uplink and downlink. Previous deterministic dictionary has utilized deterministic basis, such as discrete Fourier transform (DFT) or orthogonal DFT (ODFT) basis, which tend to represent noise interference as part of channel characteristics. Furthermore, this deterministic dictionary is not able to adapt to dynamic communication environments. However, dictionary learning has shown the potential to significantly improve the accuracy of channel representation. Nevertheless, current research on training dictionary lacks analysis regarding constraints and boundary requirements, resulting in a suboptimal basis. To address this issue, conditional constraints associated with joint dictionary for channel representation are analysed. To screen for optimal basis, the joint dictionary is subject to constraints, including uplink and downlink constraints. Furthermore, the authors aim to quantify the maximum boundary of joint dictionary learning. Additionally, a joint dictionary updating method with singular value decomposition under constraint boundary conditions is proposed. Simulation results demonstrate that the proposed CJDL algorithm provides a more accurate and robust channel representation.

Forming Massive Terrestrial Satellites through Binary-exchange Capture

The number of planetary satellites around solid objects in the inner solar system is small either because they are difficult or unlikely to form or because they do not survive for astronomical timescales. Here we conduct a pilot study on the possibility of satellite capture from the process of collision-less binary exchange and show that massive satellites in the range 0.01–0.1 M ⊕ can be captured by Earth-sized terrestrial planets in a way already demonstrated for larger planets in the solar system and possibly beyond. In this process, one of the binary objects is ejected, leaving the other object as a satellite in orbit around the planet. We specifically consider satellite capture by an “Earth” in an assortment of hypothetical encounters with large terrestrial binaries at 1 au around the Sun. In addition, we examine the tidal evolution of captured objects and show that orbit circularization and long-term stability are possible for cases resembling the Earth–Moon system.

Integrated Communications and Localization for Massive MIMO LEO Satellite Systems

Integrated Communications and Localization for Massive MIMO LEO Satellite Systems

Annual improved maps to understand the complete evolution of 9 thousand lakes on the Tibetan plateau in 1991–2023

Rapid changes in the densely distributed lakes on the Tibetan Plateau (TP) reflect the responses of terrestrial water resources to climate change. Timely and accurate monitoring of lake dynamics is essential for formulating adaptation strategies to manage water and protect public facility safety sustainably. Interfered by the numerous glaciers and snow mountains and limited by the acquisition and computing capacities of massive satellite data, annual inventories of all the lakes ranging from mini to large on the TP are still lacking. Here, we annually mapped these lake areas using all the Landsat imagery, a robust algorithm for detecting surface water according to multiple spectral indices, and Google Earth Engine. We further proposed an effective approach for accurately identifying the glaciers, snow, and mountain shadows in satellite imagery by introducing the characteristics of image luminosity and terrain slope, and removing their data noise remained in the lake maps to generate an annual precise dataset (Lake_TP) of the approximately 9,000 lakes over 0.1 km2 on the TP during 1991–2023. We revealed a rapid expansion of lakes with significant spatial heterogeneity, with 6,590 newly increased and 2,851 disappeared lakes found. The total lake areas (554.1 km2/yr) and numbers (77.9/yr) continuously and significantly increased in the period. The growth in lake numbers dominated by small lakes mainly happened before 2005, while the increases in lake areas dominated by large lakes lasted the whole period after 1995. The most significant increases in lake areas and numbers happened in the north of the Inner Basin and Yangtze, the hotspot of lake changes identified in the study. The dataset is expected to promote our understanding of the complete lake evolution process and the dynamic response of the cryosphere to the changing climate. The method proposed is also applicable to continuously monitoring the dynamics of lakes with higher accuracies in other alpine regions around the world. The Lake_TP dataset is publicly available at https://doi.org/10.5281/zenodo.10686952 (Zhou et al. 2024).

Myxoma: An Unusual Aggressive Orbital Lesion.

Myxoma is a rare tumor that can be challenging to diagnose, with imaging findings that can be nonspecific. We present a case of a 21-year-old man who presented with a subacute history of right visual deterioration and proptosis. Imaging showed a large right superomedial orbital mass of 43 × 31 × 24 mm, which enhanced heterogeneously and was eroding the adjacent orbital roof and medial wall. An excisional biopsy was performed via a lid crease approach under transorbital endoscopic guidance. We review the clinical, radiological, and histological characteristics of myxoma. In addition, we highlight important associations with genetic syndromes including Carney complex and Mazabraud syndrome.

Non-infectious hypertrophic pachymeningitis associated with orbital inflammatory disease: a pooled analysis.

To describe four cases of non-infectious hypertrophic pachymeningitis (HP)-associated with orbital inflammatory disease (OID). This study summarises the clinico-radiological features, outcomes, and management of HP-associated OID. Retrospective case-series of patients with radiological evidence of HP and OID. Comprehensive literature review of all published English-language non-infectious causes of HP-associated OID. Reference lists were screened for inclusion of relevant articles. Thirty-seven cases of HP-associated OID (Mean age: 49.2 ± 17.4 years old; Male: 15) were identified, including four cases from our institution. Aetiologies included ANCA-associated vasculitis (12/37), non-specific/idiopathic (11/37), IgG4/multifocal fibrosclerosis (11/37), neurosarcoidosis (1/37), inflammatory myofibroblastic tumour (1/37), and giant cell arteritis (1/37). Orbital pain, headache, visual deterioration, and cranial nerve palsies were common clinical presentations. Both "focal" and "diffuse" HP were observed, with the most common sign of orbital involvement being an inflammatory orbital mass, typically with orbital apex involvement. Orbital myositis and dacryoadenitis were less common. The cavernous sinus was the most common site of extra-orbital inflammation. There was no single differentiating specific radiological feature between non-specific and specific forms of HP-associated OID. The clinico-radiological manifestations of HP-associated OID differ from those described in isolated HP or OID. There is no single specific radiological marker differentiating non-specific/idiopathic disease from secondary causes; however, the co-existence of HP in OID should prompt suspicion of an underlying cause. The disease may be refractory or resistant to initial treatment, although guidelines surrounding its management and the long-term prognosis remain to be determined.

A Case of Malignant Transformation of an Orbital Epidermoid Cyst to Cystic Squamous Cell Carcinoma.

Squamous cell carcinoma of the orbit is uncommon as there is no squamous epithelium in the orbit. Thus, mechanistically squamous cell carcinoma of the orbit most commonly arises from a cutaneous lesion. Although orbital epidermoid cysts are thought to have very low malignant potential, these lesions possess squamous epithelium and theoretically can undergo malignant transformation. Here we present the case of a 63-year-old woman who presented with a 3-month history of diplopia and forehead tenderness with an orbital extraconal lesion on MRI consistent with a ruptured epidermoid cyst. Six months following resection, she suddenly experienced new-onset left upper eyelid ptosis, recurrent diplopia, and left orbital pain. MRI revealed a recurrence of the left orbital mass. Left anterior orbitotomy and biopsy revealed cystic squamous cell carcinoma. This case appears to demonstrate a very rare malignant transformation of an epidermoid cyst to cystic squamous cell carcinoma.

Pathological findings in enucleated eyes of patients with neurofibromatosis type 1: report of a case with 15-year follow-up and review of 14 patients in the literature

BackgroundsIris nodules are frequently noted as clinical manifestations of neurofibromatosis type 1 but the other intraocular manifestations are rare. The purpose of this study is to present a patient with a phthisic eye who underwent enucleation for a cosmetic reason after 15-year follow-up and also to review 14 patients with enucleation described in the literature.Case presentationA 17-year-old man with neurofibromatosis type 1 from infancy underwent the enucleation of phthisic left eye and also had the resection of eyelid subcutaneous mass lesions on the left side for a cosmetic reason. He had undergone four-time preceding surgeries for eyelid and orbital mass reduction on the left side in childhood and had developed total retinal detachment 10 years previously. Pathologically, the enucleated eye showed massive retinal gliosis positive for both S-100 and glial fibrillary acidic protein (GFAP) in the area with involvement of the detached retinal neuronal layer, together with a more fibrotic lesion along the choroid which were, in contrast, negative for both S-100 and GFAP. The choroid, ciliary body, and iris did not show apparent neurofibroma while episcleral neurofibroma was present.Literature reviewIn review of enucleated eyes of 14 patients in the literature, buphthalmic eyes with early-onset glaucoma on the unilateral side was clinically diagnosed in 9 patients who frequently showed varying extent of hemifacial neurofibromatosis which involved the eyelid and orbit on the same side. Pathologically, neurofibromas in varying extent were found in the choroid of 12 patients. One patient showed choroidal malignant melanoma on the left side and fusiform enlargement of the optic nerve on the right side suspected of optic nerve glioma. The phthisic eye in another patient showed massive retinal gliosis similar to the present patient.ConclusionsIn summary of the 15 patients with neurofibromatosis type 1, including the present patient, buphthalmic or phthisic eyes with no vision were enucleated for cosmetic reasons and showed choroidal neurofibroma in most patients and massive retinal gliosis in two patients including the present patient.

Dust rings trap protoplanets on eccentric orbits and get consumed by them

ABSTRACT We study the orbital evolution and mass growth of protoplanets with masses $M \in [0.1{\!-\!}8]$ M$_{{\oplus }}$ in the vicinity of a dusty ring, using three-dimensional numerical simulations with a two-fluid model and nested-meshes. We find two stable, eccentric orbits that lock the planet in the ring vicinity, thereby inhibiting its migration and allowing it to accrete dust from the ring. One of these orbits has an eccentricity comparable to the aspect ratio of the gaseous disc and has its periastron within the ring, enabling intermittent accretion during each pass. The other orbit has a smaller eccentricity and an apoastron slightly inside the ring. A planet locked at the outer orbit efficiently accretes from the ring and can reach the critical mass for runaway gas accretion on time-scales $\gtrsim 10^5$ yr (for a 10 M$_{{\oplus }}$ dust ring at 10 au), while a planet locked at the inner orbit has a slower growth and might not supersede the super-Earth stage over the disc lifetime. While in our runs a low-mass embryo forming within the ring eventually joins the outer orbit, it is likely that the path taken depends on the specific details of the ring. The trapping on the outer orbit arises from an intermittent, strong thermal force at each passage through the ring, where the accretion rate spikes. It is insensitive to uncertainties that plague models considering planets trapped on circular orbits in rings. It is highly robust and could allow a growing planet to follow an expanding ring over large distances.

The Orbit and Dynamical Mass of Polaris: Observations with the CHARA Array

The 30 yr orbit of the Cepheid Polaris has been followed with observations by the Center for High Angular Resolution Astronomy (CHARA) Array from 2016 through 2021. An additional measurement has been made with speckle interferometry at the Apache Point Observatory. Detection of the companion is complicated by its comparative faintness—an extreme flux ratio. Angular diameter measurements appear to show some variation with pulsation phase. Astrometric positions of the companion were measured with a custom grid-based model-fitting procedure and confirmed with the CANDID software. These positions were combined with the extensive radial velocities (RVs) discussed by Torres to fit an orbit. Because of the imbalance of the sizes of the astrometry and RV data sets, several methods of weighting are discussed. The resulting mass of the Cepheid is 5.13 ± 0.28 M ⊙. Because of the comparatively large eccentricity of the orbit (0.63), the mass derived is sensitive to the value found for the eccentricity. The mass combined with the distance shows that the Cepheid is more luminous than predicted for this mass from evolutionary tracks. The identification of surface spots is discussed. This would give credence to the identification of a radial velocity variation with a period of approximately 120 days as a rotation period. Polaris has some unusual properties (rapid period change, a phase jump, variable amplitude, and unusual polarization). However, a pulsation scenario involving pulsation mode, orbital periastron passage, and low pulsation amplitude can explain these characteristics within the framework of pulsation seen in Cepheids.

A 5-Year Clinical Experience of Pediatric Ophthalmic Ambulatory Surgery Under General Anesthesia From a Chinese Tertiary Children's Hospital

PurposeAmbulatory surgery (same-day or day surgery) is an efficient medical practice. However, there were few reports regarding the safety of ophthalmic ambulatory surgery for children under general anesthesia. This study aims to explore its clinical complications. DesignA retrospective observational study. MethodsThe clinical data of pediatric patients who received ambulatory ophthalmic surgery under general anesthesia at the Children’s Hospital of Fudan University from January 2015 to December 2019 were analyzed retrospectively. Postoperative complications, unplanned reoperation, delayed discharge, and other adverse events were analyzed. FindingsConsecutive patients (N = 4,616) had an average age of 4.6 ± 2.6 years. The primary surgical procedures included chalazion incision and curettage (62.89%), strabismus surgery (18.98%), trichiasis surgery (14.36%), eyelid or orbital mass resection (2.49%), blepharoptosis surgery (0.91%), and other procedures (0.37%). The average operative time was 25.28 ± 20.45 minutes (n = 2,698), while the average length of hospital stay was 8.45 ± 2.61 hours. No serious adverse events or death happened. One case had delayed postoperative hemorrhage, one had a postoperative infection, and two had delayed discharge. The rate of unplanned reoperation was 0.39% 90 days after surgery, with recurrence of chalazion and postoperative complications of ptosis as the primary reasons. ConclusionsPediatric ophthalmic ambulatory surgery under general anesthesia is a feasible and efficient operation mode with few complications for simple procedures with good general conditions. Further randomized controlled studies are needed to provide strong evidence of the safety and socioeconomic efficacy of this mode.

Metabolic characteristic profiling of 1-amino-3,3-dimethyl-1-oxobutan-2-yl-derived indole and indazole synthetic cannabinoids in vitro

Characterizing the metabolic profiles of synthetic cannabinoids (SCs), a type of new psychoactive substances, is of particular importance for forensic detection and analysis. Although the metabolism of individual SCs derived from 1-amino-3,3-dimethyl-1-oxobutan-2-yl (ADB-SCs) has been reported, their metabolites also undergo a continuous change and combination of their tail and core regions. Therefore, elucidating the metabolic characteristics and effects of these structures is essential to enhance our understanding. In this study, the human liver microsome was used as the model for studying the in vitro phase I metabolism of 12 ADB-SCs, and the metabolites obtained were analyzed using ultra-high performance liquid chromatography–tandem four-level rod-electrostatic field orbital ion trap mass spectrometry to determine type, structure, and relative contents. The results indicated that hydroxylation and N-dealkylation were the major metabolic pathways in 12 ADB-SCs. The effects of the core and tail on the metabolism of these ADB-SCs were studied using theoretical calculations. For N-dealkylation metabolism, the strong electron-withdrawing conjugative effect of the –N= moiety in the pyrazole ring, steric hindrance of the tail, and electronic effect of substituents on the tail significantly affected metabolism. Further, it changed the relative contents of N-dealkylation metabolites. For hydroxylation, the reaction types were inconsistent at different parts. For instance, the phenyl group of the core is electrophilic, and its electron cloud density determines whether the phenyl group can be hydroxylated at the specific metabolic sites. Meanwhile, hydroxylation of the neopentyl moiety of the linked group involves the oxidation of aliphatic C–H bonds, whereas amide–hydroxylamine tautomerism affects hydroxylation metabolism. When the alkyl chain in the tail contains functional groups (such as –F and >CC<), oxidative defluorination or dihydrodiol metabolites are produced. Taken together, we systematically determined d the effect of functional groups in the core and tail of ADB-SCs on their metabolism, validating confirmed the feasibility of ADB-SC metabolism prediction based on their structural characteristics.

Clinical analysis of 37 Chinese patients with ocular amyloidosis: a single center study

ObjectiveTo examine the clinical characteristics, diagnosis and treatment, and prognosis of ocular amyloidosis in a Chinese population.MethodsA retrospective case series study was conducted. The clinical data of 37 patients with ocular amyloidosis were collected and the clinical characteristics, diagnosis and treatment, and prognosis were summarized and analyzed.ResultsThe 37 patients included 12 males and 25 females ranging in age from 22 to 75 years, with median age of 49 years. The clinical signs and symptoms included a conjunctival mass in 37 patients (100%), periorbital discomfort or pain in 29 patients (61.9%), ptosis in 18 patients (23.8%), exophthalmos or eyeball displacement in 3 patients (14.3%), restricted eye movement in 2 patients (9.52%), vision loss in 1 patient (4.76%), and diplopia in 1 patient (4.76%). A total of 29 patients had only conjunctival involvement and 8 patients had concomitant orbital and conjunctival involvement. The main treatment for patients with conjunctival involvement was surgical resection. Thirty-one patients had stable disease, 4 patients progressed or relapsed, and 2 patients were lost to follow-up.ConclusionOcular amyloidosis most commonly presents as an eyelid or conjunctival mass or diffuse thickening and can also present as an orbital mass. Diagnosis is mainly dependent on histopathological examination. Surgery is the main treatment and is done to confirm the diagnosis to guide further treatment, preserve function, and prevent complications that threaten visual acuity. Close postoperative follow-up is necessary.

Architecting CubeSat constellations for messaging service, Part I

In today’s modern and globalized world, connectivity is a key factor for businesses, production facilities, sensor networks, and ordinary people. However, there are still populated areas which are not covered by ground-based telecommunications infrastructure. This is where telecommunication satellite constellations come in, as they can provide coverage to remote and uninhabited regions and fill existing connectivity gaps to ensure data transfer.LoRa is one of the technologies designed for data transmissions over long distances with low power consumption. Alongside with other technologies of the Low-Power Wide Area Network family, it is widely used for Internet of Things applications. LoRa chirp spread spectrum modulation is robust against the Doppler frequency shifts encountered in low earth orbits, and it has already been used in IoT satellite communications. Due to the low transmitted signal power, the achieved data rate is not high, making it a suitable technology for telecommunications payloads on CubeSat platforms for messaging services. As compared to existing traditional communication satellite systems, CubeSat constellations are low-cost and may offer an affordable connectivity service to developing regions.This study is divided in two parts. In Part I the demand model is built based on the population distribution not covered by cell towers. The LoRa link performance is analyzed, considering the impact of LoRa channel parameters variation, such as spreading factor and channel bandwidth, while satellite orbital height, transmission antenna beamwidth, and transmitter peak power have a direct impact on the payload mass. Among thousands of possible configurations, 73 feasible payload designs have been downselected. In Part II of the study, the satellite mass and the total system cost are estimated based on the payload parameters obtained. Messages transmission simulation via a constellation is conducted in order to identify optimal constellation architectures for messaging service, as well as the main drivers of the system economic profitability.The presented analysis results provide a deeper understanding of LoRa connectivity advantages and limitations together with the performance drivers, which will support the optimization of future LoRa-based satellite communication systems and other IoT satellite constellations.

A quasar-galaxy merger at z~6.2: Rapid host growth via the accretion of two massive satellite galaxies

We present JWST/NIRSpec integral field spectroscopy in the rest-frame optical bands of the system PJ308--21, a quasar at $z=6.2342$ caught as its host galaxy interacts with companion galaxies. We detect the spatially extended emission of several emission lines ( and ), which we used to study the properties of the ionized phase of the interstellar medium: the source and hardness of the photoionizing radiation field, metallicity, dust reddening, electron density and temperature, and star formation. We also marginally detected continuum starlight emission associated with the companion sources. We find that at least two independent satellite galaxies are part of the system. While the quasar host appears highly enriched and obscured, with photoionization conditions typical of an Active Galactic Nucleus, the western companion shows minimal dust extinction, low metallicity ($Z and star formation driven photoionization. The eastern companion shows higher extinction and metallicity ($Z compared to the western companion, and it is at least partially photoionized by the nearby quasar. We do not find any indication of AGN in the companion sources. Our study shows that while the quasar host galaxy is already very massive dyn it is still rapidly building up by accreting two relatively massive star companion sources. This dataset showcases the power of JWST in exposing the buildup of massive galaxies in the first gigayear of the Universe.

Dynamic analysis of the tethered satellite system considering uncertain but bounded parameters

Dynamic analysis of the tethered satellite system (TSS) can provide a fundamental guideline to the evaluation of performance and robust design of the system examined. Uncertainties inherited with the parameters would induce unexpected variation of the response and deteriorate the reliability of the system. In this work, the effect of uncertain mass of the satellites on the deployment and retrieval dynamics of the TSS is investigated. First the interval mode is employed to take the variation of mass of satellite into account in the processes of deployment and retrieval. Then, the Chebyshev interval method is used to obtain the lower and upper response bounds of the TSS. To achieve a smooth and reliable implementation of deployment and retrieval, the nonlinear programming based on the Gauss pseudo-spectral method is adopted to obtain optimal trajectory of tether velocity. Numerical results show that the uncertainties of mass of the satellites have a distinct influence on the response of tether tension in the processes of deployment and retrieval.

Data Quality Assessment of Gravity Recovery and Climate Experiment Follow-On Accelerometer.

Accelerometers are mainly used to measure the non-conservative forces at the center of mass of gravity satellites and are the core payloads of gravity satellites. All kinds of disturbances in the satellite platform and the environment will affect the quality of the accelerometer data. This paper focuses on the quality assessment of accelerometer data from the GRACE-FO satellites. Based on the ACC1A data, we focus on the analysis of accelerometer data anomalies caused by various types of disturbances in the satellite platform and environment, including thruster spikes, peaks, twangs, and magnetic torque disturbances. The data characteristics and data accuracy of the accelerometer in different operational states and satellite observation modes are analyzed using accelerometer observation data from different time periods. Finally, the data consistency of the accelerometer is analyzed using the accelerometer transplantation method. The results show that the amplitude spectral density of three-axis linear acceleration is better than the specified accuracy (above 10-1 Hz) in the accelerometer's nominal status. The results are helpful for understanding the characteristics and data accuracy of GRACE-FO accelerometer observations.

Ubiquitous Integrated Sensing and Communications for Massive MIMO LEO Satellite Systems

Ubiquitous Integrated Sensing and Communications for Massive MIMO LEO Satellite Systems

Evolutionary nature of puffed-up stripped star binaries and their occurrence in stellar populations

The majority of massive stars are formed in multiple systems, and at some point during their life, they interact with their companions via mass transfer. This interaction typically leads to the primary shedding its outer envelope, resulting in the formation of a “stripped star”. Classically, stripped stars are expected to quickly contract to become hot and UV-bright helium stars. Surprisingly, recent optical spectroscopic surveys have unveiled many stripped stars that are much larger and cooler, appearing “puffed up” and overlapping with the Main Sequence (MS) in the Hertzsprung–Russell diagram. Here, we study the evolutionary nature of puffed-up stripped (PS) stars and the duration of this enigmatic phase using the stellar-evolution code MESA. We computed grids of binary models at four metallicities: Solar (Z⊙ = 0.017), Large Magellanic Cloud (LMC, Z = 0.0068), Small Magellanic Cloud (SMC, Z = 0.0034), and Z = 0.1 Z⊙. Contrary to previous assumptions, we find that stripped stars regain thermal equilibrium shortly after the end of mass transfer and maintain it during most of the PS phase. Their further contraction towards hot and compact He stars is determined by the rate at which the residual H-rich envelope is depleted, with the main agents being H-shell burning (dominant for M ≲ 50 M⊙) and mass-loss in winds. The duration of the PS star phase is approximately 10% of the core-He burning lifetime (1% total lifetime) and up to 100 times more than the thermal timescale. It decreases with increasing mass and luminosity and increases with metallicity. We explored several factors influencing PS star lifetimes: orbital period, mass ratio, winds, and semiconvection. We further carried out a simple binary population synthesis estimation, finding that ∼0.5–0.7% of all the stars with log (L/L⊙) &gt; 3.7 may, in fact, be PS stars. Our results indicate that tens to hundreds of PS stars in post-interaction binaries may be hiding in the MS population, disguised as ‘normal’ stars: ∼100 (∼280) in the SMC (LMC) and ∼1500 in the Milky Way. Their true nature may be revealed by spectroscopically measured low surface gravities, high N enrichment, and likely slow rotation rates.